I slept in a recliner for more than ten years because of my back! (I can not lay flat) Eventually I got an adjustable bed about 3 or so years ago and I sleep in roughly the same position as the recliner. All of my six in house sleep studies was done in an adjustible bed in that position, except for one study, and that study I actually slept in a oversized recliner, it was heaven the most comfortable recliner I had ever sat in or shall I say slept in. But even in a recliner sleeping in a "Fowlers" position, I still had severe complex sleep apnea with extremely low O2 saturations! When I worked in the hospital ( I was an RN on an Oncology unit, I am now on disability) many times patients with respiratory problems would sleep in a Fowlers position, it was much more comfortable for them to breath and be able to get to sleep! And although it can help some people with OSA, it will not necessarily prevent it, nor stop it completely! But for some it can help, for me sleeping like that is a necessity, because of my back and yet I still have sleep apnea, and I use the ResMed VPAP ASV machine with 3LPM of supplemental oxygen, using the Respironics Fit Life full face mask.
Some BP medicines do cause a chronic cough. I learned this while working in hemodialysis. The prescribing doc should know about the cough as there should be an alternate medicine.