I think that's because the screen is a bit curvy at the edge. Anyway why would u want tempered glass anyway. I've been using lumias for years and never had a single scratch anyway.

The 950XL 4 corners are curved. Using cheap tempered glass will result the 4 corners to bubble up. I am using the Nilkin's one, higher price but fit perfectly because the tempered glass also designed with curves at the corner. Roughly remember is in the range of 40-50 but to me it is well worth the price, the quality difference is huge.

Edit : I bought mine from Taobao Nilkin shop.

are you placing it in a pouch or a case?

At times, the edges are pinched hence the tempered glass lifts from its original position. Placing it on a car holder has the same effects by the side, where the holder grips

price and where to get please.. haha
interested