I too play in locations where I cannot set the speaker behind me.
This is what I currently do with my Bose L1 Compact:
1. Set it to one side or the other of the keyboard, and within several feet of the end, depending on how much space is available.
2. Line up the Compact's back with the front-most tips of my keyboard stand (this is about in line with the audience side of the keyboard). This puts it a little forward of my ears so I won't hear so much bass (I am usually set up with a wall very near to my back, which can amplify the bass tones if the Compact is too close to it).
I don't hear quite the same thing as the audience, but my consistent setups help me calibrate volume etc. based on experience. As part of my setup, I walk around the room and listen while something is playing. I also invite feedback regarding the volume to help calibrate my ears.
Adjusting bands 1 & 2 of the Master EQ (PSR-S975) up or down a little helps me get the bass "dialed in" for the room.
Other solutions/techniques likely exist that I haven't discovered yet. I would love to hear what other gigging players do/have done with their Bose L1 Compacts.
- Royce