Ive noticed the same thing.. in fact even when rolling myself i notice a huge difference in the amount of kimuras i catch from the bottom compared to how many i catch from top.. but i didnt know if it was bc of the mechanics or if starting from side control might increase your kimura percentage from the bottom once you roll into it already locked in? But now that my question is answered.. is there a reason its preferred to be on top? (assuming its jiujitsu and not MMA) or is it just personal opinion? for me i just like bottom because i feel i have a larger arsenal of moves to work with based on what i know.. but lets say once i improve my top game.. whats the main reason its better to be on top?