For me, it depends on two things mostly. One, how long I go before the last time I came was. If I go a few days my loads are always huge. But two, how good it feels and/or how turned on I am. If I am super turned on, it just feels better, and my orgasms are more powerful and I can shoot some big ropes that are just amazing. Or, if it feels amazing. Example, a quick three minute session with my right hand and I may not even produce a major rope, and the pulses of each shot are not super pleasurable.
But if my FWB is getting me off either by fucking me or giving me head... dear god that girl can please a man and I cum so hard every time. Or if I am using like a bullet vibrator on my dick, it feels out of this world insanely good, and I cum hard af and it gets everywhere.
So yeah, time and level of pleasure always affect my loads.