Hi. This is going to be a bit long.
And what am I going to say will make the most sense to you if you have this test running so you can see visually what I am talking about.
Also keep the service menu open as well to guide you.
http://www.testufo.com/#test=photo&phot ... &height=-1
You're using a VT Tweak in that example, so the maximum strobe phase allowed here will be 49.7.
The higher the strobe phase, the LOWER the maximum strobe duty will be (the lower the persistence).
This is easy to figure out if you know the math and math isn't hard.
For all monitors (not just Benq), refresh rate persistence (input lag, response time, whatever you want to call it) is:
1000 / refresh rate, answer is in milliseconds.
1000 / 60 = 16.7 ms
1000 / 100= 10 ms
1000 / 120= 8.3ms
1000 / 144= 6.9 ms
Maximum strobe phase = (Refresh rate persistence / minimum strobe persistence).
by default, the minimum strobe persistence depends on the refresh rate, and is equal to the refresh rate persistence divided by 100 (yay more divisions).
Minimum strobe persistence is a strobe duty of 001. It's the base persistence for strobing, and the total persistence is equal to base persistence * strobe duty value.
So again assuming default operation (no VT tweaks),
16.7 ms / 100 = 0.167 (base persistence for 60hz)
10 ms / 100 = 0.1 ms (base persistence for 100hz)
8.3ms / 100 = 0.083 ms (base persistence for 120hz)
6.9ms / 100 = 0.069ms (base persistence for 144hz).
As you can clearly see, if you plug in (maximum strobe phase = refresh rate persistence / minimum strobe persistence),
you get "100" every time. And sure enough in the Benq service menu, the maximum strobe phase is 100. It all adds up.
However, when you use a Vertical Total tweak, when the VT is being run out of specification, the monitor reverts to 60hz pulse widths, thus 0.167ms base persistence, even at higher refresh rates. Why does this happen? I don't know. It just does it. So instead of the pulse width (base persistence) depending on the refresh rate, it becomes a FIXED value of 0.167.
As you can see by plugging in the numbers again, this LIMITS the maximum strobe phase. So : for 120hz: 49.7 = (8.3 divided by 16.7).
This is where everyone gets confused.
NORMALLY, when the maximum strobe phase is 100, strobe duty's valid ranges can be set from 1 to 30 (base persistence * 001 through base persistence * 030). Even when strobe phase is 100. There seems to be a buffer of some sort that allows this.
However, when the maximum strobe phase is limited to a LOWER value, this causes the maximum strobe DUTY to also be limited. Meaning as you raise the strobe phase, the persistence also gets lowered (the screen gets dimmer). I believe this is because you are strobing in the current frame instead of the previous frame, and the "buffer" that existed to allow a strobe duty of 1-30 at a full strobe phase of 0-100 is removed. I believe this buffer why strobe phase starts at "000" instead of "001", because 0-100 is 101 values.
So in your example, Strobe phase 043+duty 007 will be BRIGHTER by 0.167 ms of persistence than strobe phase 044 and Strobe duty of 006.
the response time will be the same.
However there will be MORE crosstalk at the BOTTOM of the screen by a few pixel lines, with a strobe phase of 043 than strobe phase of 044.
Remember what crosstalk is?
Crosstalk is the mixing of the frame data from the next frame with the frame data of the current frame at the same time, on the same pixels. With a "high" strobe phase, the pixels towards the top of the screen will be the "current" rendered frame while the pixels towards the bottom of the screen will be the *NEXT* rendered frme. Since "Next" = later, it's obvious (since monitors refresh top to bottom) that there's more input lag at the bottom of the screen than the top. I hope this is self explanatory.
As you LOWER the strobe phase, you are "moving" the next rendered frame higher up the screen and pushing the current rendered frame up, making that area smaller, and then increasing the crosstalk (which will be that horribly blurry field separating the two frames). As your drop the strobe phase down to 000, the next rendered frame now covers the entire screen (meaning you are dealing now with 1 frame of higher input lag total) and the current rendered frame is completely pushed off the top of the screen. There is now some new crosstalk at the bottom of the screen, which is the next rendered frame +1 (two frames of input lag).
The reason why if you go past strobe phase 049, the backlight shuts off, is because you can't decrease input lag of the current rendered frame. There is no such thing as a previous rendered frame that occurs BEFORE the current (true time) rendered frame, and when you increase the strobe phase, the data at the "bottom" of the screen which is the current frame, gets pushed up and covers more of the screen. Since there is no 'previous' rendered frame left, the strobe persistence gets lowered as there's nothing left to strobe, basically. Once you reach strobe phase 049, you're at the absolute limits of the monitor's own response time, which is 0.167 millliseconds. Go any higher and you exceeded the monitor capabilities and the backlight shuts off, because it can't strobe any faster.
tl;dr:
You need to look at the crosstalk at strobe phase 043+ strobe duty 007 vs strobe phase 044 +strobe duty 006, vs strobe phase 045 + strobe duty 005.
As the strobe phase gets higher, the max brightness/persistence is lowered but the crosstalk is lowered also.
Decide on the balance of crosstalk vs brightness. Whatever you find acceptable for image quality in your game is what you should use.
About the strobe utilty?
To be honest, if you are using a VT tweak, the strobe utility caps the maximum strobe phase at 047 anyway, so to be honest, it doesn't matter. the strobe utility is based on people using a VT Tweak at 120hz refresh rate.
However if you are NOT using a VT tweak at all, OR if you are using 100hz with a VT tweak, then a max strobe phase of 047 is a problem for crosstalk. For 100hz, you probably want a strobe phase of 053 (strobe duty 007) or 054 (strobe duty 006) as the backlight shuts off at Strobe phase 060. So yes, once you are experienced with these settings, using the Service Menu is a better idea.
the strobe utility is based firmly on 120hz with a VT tweak. And yes, "earlier strobe phase" in the windows utility should be "later strobe phase" on the left and "earlier strobe phase" on the right, but that's a different story.