Best Practice AP Mounting

Hello all,
I am looking for best practice mounting of 4 STX5HPnDR2 Access points onto a single mast. Each antenna being a 90 degree sector how much vertical spacing should be between each antenna for optimum operation? This is a small Rohn 25 tower with a 15’ mast out the top. And for future what would be the horizontal spacing if I was on a water tower and have more room?
Thanks, James

I would suggest 1m spacing if you can afford it. Some metal sheets between them will help a bit too.