This thread is not ideally for display engineering style questions. Those should be posted in Area 51, and not in this GSYNC 101 tweaking HOWTO. This discussion may later (in the next few hours) be moved to Area51 once you've read the reply.
<TECHNICAL REPLY>Advanced Reading for Advanced UsersScanout diagram A
However, scanout diagram A needs to contains some thin slices of minimum-possible VBI blanking interval, so corrected diagram A for both VSYNC OFF as well as GSYNC+VSYNC OFF for the situation of continuous "frame-time < refresh-time" (framerate permanently above hz):

The relevant Blur Busters themed scanout diagram is:

The same situation happens with 360fps during 120Hz GSYNC+VSYNC OFF and 120Hz FreeSync+VSYNC OFF. There are implementation differences behind the scenes for GSYNC/FreeSync but the scanout behaviour (because that's where matters from a human vision & latency perspective: displays painting the refresh top-to-bottom, so top edge of a refresh cycles have photons hitting eyes first) is the same; a new refresh cycle cannot be started until right after the minimum-specified VBI size. For FreeSync, the minimum VBI size is dependant on the EDID/DisplayID advertised by the monitor or the custom resolution configured as the current Vertical Total. FreeSync/HDMI VRR/VESA AdaptiveSync -- all interoperably enlarges/reduces the Back Porch (embedded in the Vertical Total number) changing every single refresh cycle to dynamically space the refresh cycles apart, but can be never be below the minimum allowed number.
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