Try entering at a reduced throttle setting, when you get to the 7 oclock, full power untill 11 oclock, off the power over the top, full power at 3 oclock untill exit.
once you get to 11 oclock you can be getting of the rudder only getting back one at the 3 oclock position. May be even have to add a little opposite rudder over the top to flatten it out.

A true mother F..... to do with any finess.
99.9% of thoughs you see aren't correct at all.
Just go to that U-can do -3D video clip to see a total failure.
You must have the correct aeroplane to pull them of correctly plus 30 gallons of spare fuel to start the process.

Practice it in sections. Try perfecting the transition from a nice controlled knife edge pass to vertical. Then from vertical to horizontal (over the top) Then from knife edge to vertical desending, then desending to knife edge.
You'll quickly notice that each section has a completly different set of demands/stick positions/mind set etc. Completly different to each other. They are infact 4 totally independent things.
Untill each one is mastered you'll never string all 4 together. Enjoy.