As seen in the anime, Lily Enstomach grew herself into the size of a giant inside Luffy thus giving Luffy immense power. He was strong with a weakness of becoming slower. However, when he went into 2nd gear, the sheer power of turning into 2nd gear caused everything around him to be thrown back.
So does the size determine the amount of initial power the person has?
-The reason why I said initial was because power really matters on the training rather than the power of the devil fruit
Luffy, when he got bigger, the effect of 2nd Gear was stronger. Let's say that Buggy's devil fruit (section-section) gives Buggy the ability to split and fly a range 25 meters around his feet. If Buggy was the size of a giant or the size of Whitebeard, would the range increase?
This is not about how much the devil fruit is eaten.