I'd say that the setting the L1 only 7 feet behind you with a louder band is not enough. I suspect to get the volume you need with even a reasonably loud rock band you would have to set it at least 15-20 feet behind to avoid excessive feedback.
You are stuck between the rock and hard place of the sound pressure level you need and the inverse square rule that limits how quickly it dissipates before reaching the microphones.
For example, at a gig a few years back I had to cover 350 people in a large hall, we had to physically move large pieces of the stage from the side to add to the front of the stage to put the lead singer/acoustic guitar on his own platform in order to get the 12 feet plus distance I needed to fill that hall without the lead vocal feeding back.
Have you tried putting the Bose next to the band?
I know folks often get hung up in symmetry. When positioning a band on a stage the tendency is to spread everyone out so that they fill the stage width with the mass centered. Your issue is that your stage is 24' wide but ONLY 10' deep. I suspect that there's no way you're going to be able to get the Bose back far enough on your stage to avoid feedback. If I were you, I'd try my suggestions:
1) First try the Bose completely stage left (or right) in line with the drummer's ears (or slightly forward of them) so he/she can hear the band and then place the other three of you closer together near the opposite side of the stage. The side wash from Bose L1 systems is amazing.
2) If still getting feedback, you may have to provide a separate monitor for the drummer if you must keep the drums behind you and move the Bose forward so it's in line with the front line of microphones.
3) Or you could start a new trend and put all four of you in a line with the Bose next to you on one side or the other. Gene Krupa and Buddy Rich used to sit in the FRONT of the band!
Note: the apparent asymmetry can be visually attenuated by putting a sound transparent curtain in front of the Bose location that would cut the audience's sight lines down to just the band.