I like to meet in the middle and just put 1/2 inch or so of substrate enough so they can cover themselves to feel secure and not too much where debtis can get caught
Depending on what color......many of us ray keepers use torpedo beach by caribsea.......its smooth and wont hurt ur rays and its a thicker sand so u dont have to worry about powerheads and such moving it around as much although the rays will shift the sand reguardless.
Also try repositioning ur powerheads so they arent facing towards the bottom or substrate