I dont know the technical reasons why or how the covered speaker works, sorry! I’ve used both kinds and haven’t had issues with either.
Like you I am waiting for FloLabs 3D edge though, I emailed them about it because their website is extremely unclear and they said the protector I was asking about didn’t have a 3D edge (I specifically asked about the one time pro nanoarmour for the 17pm) and I asked if one might be coming but they totally glossed over that question and didn’t answer it. So I’m going with the Amazon option in the original post for now while I wait to see if FloLabs adds the 3D edge ‘upgraded’ option like they did for the 16pm last year. The fact that they didn’t have it ready to go for launch is odd, I feel like it’s a possible money grab to have people buy one now then buy another when the ‘upgrade’ comes in a couple months.
I also have a belkin screen protector left over from my 16pm that may or may not be the correct size for this years phone..