Sensitive as in they're surge fish and like a lot of current. Achilles are hard to get eating as well and hard to find at that size. They seem to come down with ich just from looking at them wrong lol. You could probably get away with the other ones for a while but like hank said emperors get massive.
20 Gallon SPS reef
29 Gallon FW "fat catfish" tank
20 Gallon Long Dart Frogs "Zig" and "Zag"