: Patsy
Don't give up. When you find it the light will go on. My theory is that you are trying to plane a concave area.... an area the plane will span and not hit with the blade. (Sounds like what you said) You can follow any number of types of advise given before, but also try this.. Instead of planing with the plane sides parallel to the direction of planing, put it diagonally as much as you can. This will effectively shorten the contact area of the planes sole and get the blade closer to the wood.

To check it, just lay the plane on the wood and crouch down and look at what is happening .... Is there a gap? Or, is the blade touching the wood. Observe as much as you can and you will find the problem. - Scott