I had a similar problem in that the drummer in my band was getting killed with slap back from bass volume in small venues and also in one outdoor setting where we would typically set up in front of a large cathedral type window and throw the sound down to a marina on a lake.
I solved both challenges by buying a 2X10 extension cab and placing it stage opposite on the outside, IE: ..... in about the same place in relation to the PA subs and mains as my 4X10 stack, but opposite side of the stage. The bottom of the stack sits on the floor. The 2X10 extension sits on the floor.
This gave the bass greater dispersal through the whole stage set up and allowed me to get the same depth and tone and run volume a couple of notches lower. The mix became better, all the band got what they wanted and needed from the bass, I hear myself better and the mix to the audience is better. The overall sound of the band is fattened and once the mix is set, no one competes for volume.
Problem solved.
Another note: I set up on stage right, next to the rhythm guitar player, who is next to the drummer. The lead guitarist is stage left. I always set the bass amp up two to three feet farther back on the stage than the rhythm player and angle my stack more straight ahead rather than to an inside angle. This gets me a bit closer to the drummer and gives me a clear line of vision to him. This angling is important, because the rhythm player most always angles his amp slightly inward so the lead player picks up the fat in the mix from him as well as from monitors. So, as I need to hear myself better, because the angles of the rhythm amp and the bass amp are different I can hear the bass better back at the amp when I'm grooving with the drummer or on the mic line when I'm singing (mostly harmonies). And, if I need to hear more from the rhythm player I can always take a step to my left and get more in his angle. Of course, if we've got a good monitor mix all this maneuvering is less necessary, but the angling is important because we seldom support the bass through the PA.
Hope this helps. If you want more detail on the equipment or other detail, let me know and I'll elaborate.
Koog.