I've been first choice gully fielder at my club ever since I broke into the 1st XI - and it came from what I was told at school - get as close as feels comfortable - then take 2 steps closer. I am usually a similar distance from the bat as the keeper (but our home pitch is a slow-low one so we're both pretty close). From there; the angle shouldn't matter too much. I take it you have decent reactions if they're picking you to field there - so just get close and cut down as much of an angle as possible. Catches are harder because you're so close, but 70+% of the stuff that comes through gully is played into the ground anyway, so just getting a hand/body in the way is saving your team runs.
Also, I reckon the split is about 50/50 every game for stuff that I can actually stop/catch and shots that are out of reach - don't move or think about it if one goes past out of reach, unless your skipper has other ideas!! Hope this helps.