Thanks Laurwin. It's opaque, makes sense, glass edges are opaqe.
Your post made me think to search for pictures of other gunsights:
Soviet PBP gunsight:
http://img717.imageshack.us/img717/3336/44968635.jpg
German Revi gunsight:
http://www.deutscheluftwaffe.de/inst...s/Revi3d-7.gif
American gunsight from P-38:
http://www.ebay.com/itm/P-38-LIGHTNI...-/110429361254
The reflector glass is always opaque, and roughly the same thickness on every gunsight. In-game, that's not the case, some consistency would be nice. I think a thin, opaque strip at the top of the gunsight would be the ideal balance between providing some depth to the gunsight edge, and not being a thick eyesore and distraction; the Mustang III gunsight is a good example.
I know that many cockpits in this game are old, need updating, and that it's a huge task. Updating a handful gunsights should be easier than updating entire cockpits and will make a big positive difference.