Thanks mate, what fish have you stocked in your 20 gallon?20 gal cube is the one I have, I edited my post up and typed and little extra info, if you mind rereading my first message.
peninsula tank would work super well if like you said both couches on either side so you can even catch the beauty of the sides!
I definitely want the best for you and when you look at fish especially 3 fish or 4 … A 20 gallon is perfect enough for all that, absolutely strive for a beautiful rock scape for all 4 fish and stuff it with corals of all colors.
I’m super glad I can help and if you do plan for a Red Sea max nano… we welcome you to the family, there are Facebook groups of Red Sea max nano that we support all and every owner. Hope to see your tank!