MK2S and glass on heatbed  

MK2S and glass on heatbed

Hi,
I just received my pre-assembled MK2S.
I tried to install a glass (bought with the printer) on the heatbed plate. First, the glass is 20x20 but the plate is 25x25, it's quite strange, not 😯 ?
Second and worst. Each time I'm trying to print something, the head touches roughly and bends the plate, so I had to reset immediatly the printer and redo a Z calibration without the glass.
Because of that, I tried every menu and finally had to do a full calibration XYZ after a "reset". Not so bad to learn how Prusa works 😉
What I understand is : the MK2S has a special plate, and a sensor on the head to detect position. Nice. But it only works if there is nothing (except PEI sheet) between the sensor and the plate.
So here my questions :
1/can I use a glass over the plate with MK2S ?
2/if yes, how to add 2.97mm to Z to avoid crash with the plate ?
3/how to do calibration tests with the glass ?
4/if it is not possible to do calibrations with the glass, how to disable "9 pts auto-calibration" on every print ❓ ?

Thanks,
David