Which avr? Yamaha(and their stoopid propriety language) does call their height/top speakers “presence” I believe. And yes, you can definitely use the BS for that purpose. As far as being on the back wall, that’s up to you to try, but if you can find speakers cheap enough, why not? Ideally no, you’d want to make sure to be off of the wall but rooms aren’t ideal so... Try .2 as front height/top first and see what you think. It might be good enough. .4 IS better in a proper layout, but again, if you can try it for cheap...