I think the best advice I've seen is the 24x24 minimum width and height. I would add to that and say length also. 24x24x24 is a nice minimum for a rank that intends to actually GROW sps colonies... not just hold frags for a month or so for blue Instagram pics then die or relocate to proper aystem, which is often what happens with those.
I currently fiind myself with sps growing within an inch of each side of my 24" wide tank. In hindsight I should have built the aquascape with the thought of only using 50-75% of the width.
Height has different issues. My tank is shallow... 16 inches... way too shallow if you like sand. Sps need high flow so I wish this tank was at least 24" tall so I could place pumps higher and hopefully they wouldn't blow my sand around. Also the more height you have the better potential for awesome vertical coral growth. With the lighting we have available today, par at depth isn't really a concern anymore.
Length really is about your available space and the number of fiah and what type and size of fish you want to keep.