Finding the best sounding firing axis angle is something that really needs to be determined by experimentation (as well as overall speaker positioning!)
Are the frequency response measurement plots available for your speakers that show different amounts of on and off axis firing angles? Ideally you would want to aim them such that the response of the top end gradually tapers off for the most pleasing sound.
Get them in the best general position from room boundaries to give you the best sounding bass and aim them straight ahead, perpendicular from the wall.
Listen for a few days with your demo songs and take notes, good, bad or other. Listen for tonal balance, brightness, sound stage, center image, etc.
Then aim them with some toe in- say 10 degrees or so (maybe ai inch from the inside front corner with tape marks. Listen again.
Repeat the process inch by inch until you get to the extreme toe angle that aims a foot or so in front of you.
Review your notes and put them in the best sounding spot!
Lots of work but that is how you get the best sound out of your speakers