First and foremost, your officer figures HAVE to stand out. At a glance, you need to know that he is not a spare infantry or cavalry stand.
For that reason, I don't base officers on square bases. They have a bad tendency of getting ranked up with the troopers, especially cavalry. Yes, I've had it happen a lot where a brigade or divisional commander blends sufficiently into a unit that he cannot be seen. I usually use round or oddly shaped bases for that reason.
Second, every commander has a staff of some sort. Cavalry brigadiers often had orderly trumpeters seconded from one of their respective units. For a brigadier, it may just be his aides de camp, though as the staff structure got formalized even a Brigadier would acquire a Brigade Major and orderly officers. Officers also had escorts, especially at Corps level. That's another great reason to put a figure on a diorama.
For the ACW, Union officers were authorized a brigade standard and somebody would carry that. Same for Division and Corps. It's a great diorama tool, and for post-1862 Union forces, I'd say nigh-on mandatory.
Finally, you always have the option of your commander conferring with some of his subordinates.
I mostly paint in 15mm, but for my RtE projects I am putting brigadiers on a 40mm round with a cavalry trumpeter or an aide de camp. Division and Corps go on 50mm rounds, with several mounted and/or dismounted figures to go on the base. Whenever I have enough for Nappy or another Army commander, I plan a REAL diorama on a 3" base. Army HQ seldom if ever moved, even if the C-in-C is out and about. Just too many staff members.