800 is pretty low for RT. You can't blame the marker much if it doesn't work. ~850 usually puts my mags at about 12 bps, ~950 is 14 bps, ~1100 is 19 bps. Ninja and crossfire regs work well, depending on the pressure you want.
The ULT has less trigger force, both in initial pull and RT. Shims help, but it's the same as grinding an RT pin down. You're shortening the sear engagement and on/off top o-ring seating. The extra pressure lets you keep more of both while using RT.