there is a direct correlation between cost of tile and level of stickness of the back. There are also several thickness of tiles too. There are some foreign makers of tile that have very little stickness on the back and are about 1/32 in thickness.
I always stress when I am laying down peel and stick tile is to get a thick tile and actually experiment with the tile and peel back a corner and apply your thumb to that area and that tile should stick to your finger and be suspended in the air.
I also always prefer to apply the tile in a room that is much hotter than the rest of the house. This actually makes the corners lie down better and makes the tile more pliable. Cold tile is like making a pringles potato chip lie flat.
Also, do not apply mastic or floor glue with peel and stick. The glue will permeate through the cracks when the slab is hot.