Oh, yes, you're correct. I would be very grateful(as the mod's current maintainer) to implement a larger portrait - folks, if any of you have experience with graphics and can provide us one, I'll be grateful, and I'm sure the players will be, too!
Playing with UB at the moment and I noticed that when Boo disappears, Minsc's portrait is replaced by a very small portrait of him. I'm currently using BG:EE, and I saw that this issue arrised in another Mod (NPC project) as old BG/Tutu/whatever used smaller portrait sizes.
Issue should be resolved by adding a bigger version of his portrait (without Boo I presume).