The only mask that works for me is scotch magic tape - the green one.
I de- tack it on my forehead or the palm of my hand then cut about 3mm of
straight strips to line the canopy frame, then just fill in the rest with the uneven
bits.
Burnish the tape with your fingernail and spray away.
The small strips go around curves nicely and if you fold over a little bit of tape on the overlaps removal is sooooooo much easier .
Another trick a friend of mine uses also uses the tape strips ,but the remaining area is covered with liquid mask.
A lot faster but doesnt always work.