I still have trouble with flying as well mate, I've flown loads of times so know I can do it but it's a little hit and miss.

I know people's Lucid's are different so was just wondering if you have very vivid, waking life quality Lucid Dreams the majority of the time?

If so that could be the reason, I've found when I have slightly lower quality Lucid's I can fly with absolute ease, however the majority of mine are waking life quality and it's in these that can be a real struggle to make my brain accept it's possible, even though I know for a fact it is.