You don’t use that one.

Use a flat one instead like this https://www.amazon.com/dp/B0968X5K4M/ref=cm_sw_r_cp_api_i_R4GJ4D1VPQT5JCFKTWBJ

I also have LPR and lower back issues. The key is to get a wedge for your legs, too. That will help ease tension on your lower back. I eventually got an adjustable bed but, before I did, I had this 10" wedge and this leg wedge. If i were doing it again, I'd go with a shorter body wedge - maybe something like 6-7". The 10" was a bit much for me.