Don't get discouraged. You can do it. True, some trainers knife edge easier than others, but stick with it, and find what it takes for your particular plane to KE. I have a WM Sky Raider Mach I trainer with an OS 40 LA on the nose. It will knife edge. I can't think of a less powerful 40 engine than the 40 LA, so raw power is not the answer.

When you enter the knife edge, make sure the plane is inclined upward slightly to help hold the KE. Good luck!