IME they like the lighting on the lower side. They're also fine if you mount them on a vertical rock face.
I would not keep a favia frag or larger colony on the sand bed long term. The lighting might be perfect there in many cases, but allowing them to be covered by sand is a no no. It's also easy for that location to have improper flow whereby bacterial films can be a problem.
Favias want to encrust and grow outwards and often build a mounded shape naturally, so put them on a rock at the right light/flow location and let them grow.