After some thought as to all the above, I laugh at myself...because this is what I was doing:
I'm been so concentrating on keeping my lower leg "On" that information I was getting from the lower legs was blotting out any attention I was paying with my hip to knee. Once I realized what I was doing, I began to pay more attention to what was happening from my knee to hip and I began to feel when my horse was not straight in the hind. Felt pretty stupid. This doesn't mean gripping with my knee, but just feeling with a soft leg. How to make things harder without really trying!