Originally Posted by lethalfang
I don't believe it's due to the mounting.
I believe it is a simple fact that, it is nearly impossible to find the perfectly equalizing tension, such that the compressing force from the mains cancels out exactly the elongating force from the crosses.
In most cases it is due to a certain type of frame (some of the Heads) and a poor mounting/support system.. or just bad mounting by the user. If you are using a Klippermate or one of lower end 2-point systems.. there is your problem. You will indeed need to stretch the frame when mounting. The question has been asked many.. many times. All the Klippermate users will swear it never happens to them. Do a Head Radical on a Klippermate and you will get compression unless you stretch the frame when mounting.
I moved from a Klippermate to a 6-point Alpha and have never seen the problem since. Not once..