the tip i normally give to people is instead of riding into it and jumping gap, try to do a rollin gap into the wall.
it should be around that kinda pace and becos ur doin a gap u dont really tuck ur bike but just bang two wheels into the wall which would mean that ur bady weight would be up and over the bars, instead of being tucked backwards in effort to get the back wheel high enough.
i hope u know what i mena.. thats how i learnt it and got it right quite consistant... (Y)
hope it helps..