I'd just experiment and see what happens. IMO, the best thing to do is to shoot a whole roll (or two) of the same exact thing, on a tripod. Try a shot as the meter tells you, followed by a shot half a stop under. Then another half stop under. Then a half stop over the first shot, then another half stop over the first shot. Then do it over and over. Keep notes as to what each exposure was. Then cut the roll into three pieces, and develop each one for a different time. Then proof the entire roll and examine the contacts to see what the changes in exposure and development did. You will get to see what an underexposure, normal exposure, and overexposure look like with normal, +10%, and +20% development.