Symbia 16° Biseau dorsal ergonomique Orthex

The product is well made, all dimensions stated on-line match and linen-mix cover looks very nice.
The reason I give only 4 stars is that we are having trouble adjusting to these wedges - this is not the company's fault. I chose this size because it is the smallest size rated for sleeping on the back and on the side. The wedge is 8.5" high and we keep sliding down (all the way to the bottom edge) while sleeping. I removed the standard pillow from the wedge and am using just a small 12" squishy down pillow, but it did not solve my problem.
I do not know if there is a way to slice the bottom layer of the wedge to bring it down to maybe 5.5".