I'd have to say the loads all about the circumstance. If the chicks fucking blazing hot and you been really staying on top of your game trying not to cum for say 30 minutes of non stop cervix bashing your gonna blow a monster. If if its your ex-GF and your just having some sloppy wine fueled slut session your probably drizzle cum out like the last few drops of milk from an empty carton.
The other thing is downward pressure, if the chick is pushing your base down when your coming your gonna let go of a shitload more cum. Next time you get a BJ have your chick stroke your cock and hold down the base real hard before you cum, you will shoot great distances and you might get lucky enough to shoot your load straight out of her eye sockets.