Cultivar Aside, what growing conditions affect bloom size....

With the warmer winter we all got and many reporting macs blooming when they never have...Im curious if weather patterns affect bloom size per cultivar

Sure, younger stems will product smaller blooms. Or when one stem has 2 laterals vs . 1 single stem with no laterals. Those I get on how bloom size can be affected. Guess I'm asking take 2 same plants, same culitvar, one produces a 6" bloom and the other produces a 12" bloom. What is the cause/effect is what my Wiki is seeking.