Fixing up the dining room and want to use 5 1/2 inch baseboard. Having trouble deciding what to do with air diffuser for heat. Current is 4 1/2 inches high. Have found one diffuser which is 6 inches high but it is very unattractive. Is it best just to cut hole size of diffuser in higher baseboard and recess or just go with smaller baseboard. I guess question is, are there any suggestions to trim around shorter diffuser when using higher baseboard?

sometimes less is more, you can run the base around the diffuser but that will make it stand out more, what id do is take a 3x4 board that is maybe a 1" taller than the baseboard. Also make sure the board is also wide enough to be able to screw the diffuser to the board, the base will be square butted into the 3x4 board.

only other way I can think of off hand is to 45 the base board where it touches the diffuser and then keep 45 cuts all the way around it. Basically making a picture frame