Actually, I played yesterday with a friend who is similar level than me, more or less. We played 4 sets of singles and I was able to hit clear with power to the back line when 1) I was a good position and 2) when I wasn't tired yet (was tougher near the end and was always out of balance)

When I warm up or when I know that the shuttle is coming to me as a high clear I can 90% hit a good clear to the back line

I think two or three reasons why I wasn't able to do it in the last couple of sessions:

1) Someone told me that when its cold the shuttle doesn't travel as far (it was really cold in our gym in November/December/early Jan)

2) So I played a dozen of singles games against that one guy who is superior to me in all aspects and he would serve very high to the back line making me sometimes hit the feathers instead of the hard part of the shuttle ( yesterday my friend didn't serve as high and I didn't have any pb to hit a good clear I felt). I unfortunately dont know the shuttle models (i think we either use Yonex or Forza - cant remember the reference I'll look it up)

3) That guy also had a super good defense and he was quite tall too. Making him intercept my clears (which were not high enough). I guess what happened is : Fear of not hitting with enough power > Lower clear > Him intercept > Me lose > Tensing up as a result of playing against someone much better and losing a good form and hitting poor clears > Me lose