Huawei p20 lite? - 1

And although I have the Huawei p20 lifts bought the same time panzerglas and a 360 degree shell The shell consists of only 2 parts a part in front and one back if I have only the front up I have no problems but as soon as I with the rear part then make is forward as if there was air under it one must also write really stronger when writing A friend of mine has the same shell but another cell phone and her is the front part of the shell flat on Why can this be?

Huawei P20 lite

Maybe on the bulletproof glass. Or because it is another brand of the shell.