I’m not really a fan of stacking the equipment like that. The sub is going to vibrate some, even if it is pretty inert cabinet/ sturdy build.
Are you measuring to center of tweeter, for your measurement? I put mine up that high because I sit very upright, and I’m tall... in that couch I’d be surprised if your ears were any more than 39-40”.
Lastly, if you want to improve that sound quality, you should pull that couch forward, and get the surrounds a little more behind your LP.
I think you should experiment with sub placement... one near you, I still like the behind the couch idea as a possible spot, and another in a different location. You can use the near side (photoperspective) end-table type placement. But subs can be finicky if you don’t find good spots for them.
That’s why you hear about the subwoofer crawl, but if you’re willing to spend money on subs, learn about how the low frequency acoustics interact with your room s little, and find the places the subs sound best!