The A80 is recommended to cover 14" square for an intermediate mixed reef. With ONLY soft corals, 20". Lift them much higher for increased coverage, your light will probably be insufficient, even given your shallow depth.
The 160's will cover up to 24", so with a tank so shallow, maybe 2 or 3 of those. You should be able to keep many sps varieties.
Here's a guy who runs a 120gal mixed reef with 4 x 160's with a fair amount of sps and a nice clam all the way on the bottom. He even puts the camera underwater for a good look lol:
www.youtube.com/watch?v=l82og1JMcuY
Edit: For our other participants to enjoy .. here's a decent 6' reef run with 3 x 360's:
Same approx light density as my 4' with 2 x 360:
www.youtube.com/watch?v=AIS25xNK8Lg&t=30s
Cheers.