P47 Canopy

Hi All,
I have built a couple of 1/48 scale P47 Thunderbolts and seem to have the same problem with them. I use the canopy provided by the kit and most of the time the fit is not right. I like to place it in the open position and it always seems to be higher in the back and not rest correctly on the model. I have seen several models whereby the canopy sits just right in the front and in the back as well. Any ideas on how to fix this problem, should I try the aftermarket canopies? Thanks for all and looking forward to hearing from you.

Which model kit do you have(Tamiya, Hasegawa, Monogram) and is it a Razorback or Bubble Top?

Guess I should have said that, but the models I use are mostly Academy, Monogram and a couple of ATM (ERTL). I have both the razorback and the bubbletop. The ones I have the most problem with are the bubbletop, the razor is not too bad. Thanks for the query.