Is this overkill on corals for a 20g ?

[Doug]

Be aware that lps corals like bubbles, hammers & frogspawns can grow much larger than a 20g footprint. They also have very potent sweepers and are almost impossible to frag, unless the branching frogspawn type coral.

Also a friends toadstool is easily over a ft. sq. but it can at least be cut down.