Your motor has way less load on it in reverse than in forward. In addition to overall pitch, Props are designed to bite and compres then flick the water off like you throw a fastball in ********. The charastics in reverse are like throwing a knuckle ball... they do not have power charastics in reverse.Look at a cut away view of a prop blade, it is shaped like a crescent moon, concave on one side, convex on the other. There are more dynamics to a prop than what I just mentioned, but no need to get into that, lets just say reverse is a combination of like trying to drill through steel with your hand drill, in reverse or using your soup spoon upside down, And The reverse cut of the prop into the water in reverse only grabs the top half of each blade on an inefficient curved edge angle . etc etc.
So rether than confusing your problem with aspects like i get full rpm and no bog down in the power curve etc. in reverse .. you provably still have a power problem,, Like a car going down hill runs fine , up hill on a real pull you will feel it.