"Changing strobe phase moves the start of the strobe from the "beginning" of the current refresh cycle (strobe phase=100) to the "END" of the current refresh cycle, in effect adding 1 frame of input lag (Strobe Phase=000)."
Close, but not always quite that simple. Assuming the backlight cut-out bug at high strobe phase numbers didn't exist, you're also bringing the _previous_ strobe flash length back, so suddenly you jump from 1 frame of input lag to 0 frame of lag. So 0 is essentially in theory exactly equal to 100 in latency, assuming it wraps around properly (assuming 100 is a full exact 8.3ms delay in strobe flash) -- because if you pushed the strobe flash length 1 full frame ahead, you've also brought the _previous_ strobe flash to exactly where it would be if it was a "0". Making "0" and "100" identical in look & input lag -- it is a wraparound effect. However, there are bugs in some monitors (like my V2 of XL2720Z) that causes the backlight to black out before the wraparound.
It's mostly a matter of _where_ on the screen you want the least screen.
In theory, excluding the fudge factor that blanking intervals provide, the average input lag of *ANY* strobe phase is all identical, if you measured the input lag of _every_ pixel on the display and then _averaged_ it all out
. So at the end of the day, strobe phase doesn't matter in input lag -- if blanking intervals were practically zero. But in the real world, we can use bigger blanking intervals (or faster scanout logic built into monitors, like LightBoost which does its own equivalent of "large vertical total" internally, bypassing Windows) that gives more flexibility in strobe phase adjustments before things become bothersome (double-image effects).
It'd be much easier to explain using images.
But you reach situations like:
--> In one setting you may have 1ms lag at top edge, 4ms in center, and 7ms at bottom edge of display
--> In different strobe phase setting, you may have 6ms lag at top edge, 1ms lag at center, and 4ms lag at bottom edge.
This non-linearity occurs when strobing occurs during the middle of scanout. So, you see, strobe phase never really increases/decreases input lag, it simply reduces input lag of one part of display, and increases input of a different part of the display.
This is due to the asymmetry of LCD scanout versus the globalness of the flash. (8.3ms scanout cycle, or rather 7.8ms scanout cycle + 0.5ms blanking interval, depending on size of vertical total; at VT1350 you got a 3:1 scanout:blanking ratio, which means ~6ms scanout + ~2ms blanking interval).
Anyway, back on topic... Crosshairs is usually in the center of the screen, so sometimes people want the strobe phase to be calibrated to the point where crosshairs has the least lag. That's sort of how BENQ monitors ship Blur Reduction by default, but it has a great cost: huge amounts of strobe crosstalk (double-image effect during fast motion) just underneath the middle of the screen. Lots of us complained to BENQ, and they fixed with the V2 firmware, by providing us with a choice of adjustability.
Now, that said -- with large blanking intervals (e.g. VT1350), there's more flexibility in where you want to time the strobe flash, so you can have a slightly earlier strobe before you begin to get bothered by strobe crosstalk.
So, if we're aiming for lower input lag AND high-quality strobing, you want the largest possible Vertical Total *and* you strobe-flash as early as possible after the scanout. "early" is relative (Einstein) ... the strobe phase numbers do not necessarily correspond to minimum lag. If the monitor had proper phase wraparound (not my monitor, the backlight cuts out at larger phase settings) wraparound point might occur at "38" during a mode, or even at "94" etc. In reality, phase is relative to the blanking interval, and there's the 1ms GtG to contend with, so ideal strobe phase is variable depending on the ratio of LCD GtG time versus the timings to delay the beginning of the active visible refresh (e.g. back porch timing)
Easiest way to do this is to run a motion test (TestUFO) while adjusting the service menu. Get the smallest number you possibly can get, without being bothered by the strobe crosstalk (double image effect) if you're adjusting for good full screen motion clarity.