I picked my screen protector for the 12.9 from the ATT store but I paid $60 at store and then ordered one for the 11" from their site for half price so check
https://www.bodyguardz.com/ first, they are pricey but they are good quality, very clear and no issues at all on my 12.9 - I'm returning my 11" today because I just couldn't find a screen protector that makes it work without issues.
The 12.9 is def issue-free compared to my 11" which needs a hand constantly touching side of bezel in order to make sure all gestures are recognized, no conductivity issue at all on my 12.9. Let me know if you end up ordering and you also have no issues.