KSF phosphors will always introduce issues regardless of whether ULMB 2 is used or not. But strobe crosstalk in general is always expected to be minimised with ULMB 2. You may not be sensitive to the issues caused by KSF phosphors as not everyone is, though I certainly am. The gold standard would really be ULMB 2 without KSF phosphors. Usually with Nvidia G-SYNC models it will be obvious whether KSF phosphors because one of the following applies:
1) It’s a standard gamut monitor (one targeting sRGB or if specified, with <86% DCI-P3 coverage as a rough guide).
2) It uses Quantum Dots to achieve a wide gamut and that is usually advertised.
3) It uses KSF phosphors to achieve a wide gamut.
The BenQ ZOWIE XL2586X and XL2546X feature the company’s third generation ‘DyAc’ technology (DyAc 2 – successor to ‘DyAc +’). BenQ is very coy on this technology and go well short of providing any technical details, but state it includes “dual backlight technology”. Based on this and marketing videos it appears to minimise strobe backlight, including just above centre, due to having more precise control of the strobe.