Not sure what masking tape you're using, but I've used
Tamiya masking tape for glue masking in the past and it's always worked well, as long as you remove it while the epoxy is still soft - leave it until the epoxy is hard and you'll get a VERY ragged edge. Other brands might not work so well. There's also
liquid masks available, though I've never tried them with any type of glue.
G.
This = Maskol latex liquid mask, usually used on small finicky areas like the glass areas on canopies of model aircraft to paint the canopy metal struts etc. (fiddly as hell)
You can leave it on for days if neccesary, though it will start to shrink at the edges - its a tad spendy in relative terms of cost vs amount you get, but a little goes a long way, 2 coats minimum to ensure coverage, dries quick though.
Another trick is to apply a first coat of the finish on the parts to be glued (or pledge, see below) - like polyurethane in your case, let dry, mask it off, then run a brush with more thinned poly along the masking edge, then if there is any creep, it'll be the same stuff as underneath and it'll seal the masking edge - old spraypainters trick that is.
Another possibility is this stuff: - loved by modelmakers the world over -
Pledge 11182 Revive It Floor Gloss, 27 Ounce, Clear Transparent Liquid : Amazon.co.uk: Grocery (so good that when it went out of production for a few years, modellers bought remaining stocks and hoarded it (I've still got maybe 3 bottles of the original stuff - but have heard this re-release is very close to the original formula)
trust me - google pledge and model making - you'll see the umpteen uses this stuff has, such as a barrier coat between non similar finishes, masking (it sands really easily), etc etc; it'll become a vital part of your modelling arsenal.
idea - you could use it painted over your canopy areas, even though you do them black, this will add a thin layer of totally transparent, glossy film that will look like glass.