Personal PA speaker behind performer

Tonight I watched a duo acoustic act with I think a Bose L1 PA positioned behind them (great as a monitor then) with no feedback! Just a small maybe 4 channel mixer for guitar and 2 vocal mics. OK is the no-feedback considering the placement, a factor of the Bose having such a skinny profile. I would like to pull that off with my AltoTrooper pa ..any hints .I assume just angle it off axis enough from my mic?
 
 
 
 
 
 
 

Yes, those things are amazing. My duo regularly uses an L1, with two microphones and an acoustic guitar going through it. We do not use stage monitors at all, they're not needed when the PA is behind you! It takes some effort to get feedback.
 
For one very small gig I even ran my keyboards through the Bose to save lugging my amps up some stairs. Those little speakers shouldered the load OK, but the main failing of the L1s is lack of highs. Perfect for vocals, and acceptable for guitar, but too dull for piano.

I have a buddy that is in a duo that uses two of these positioned behind them.  They usually don't have feedback issues.
 
The Bose L1 system, as I understand it, has some technology that eliminates feedback.  Trying this with a system that doesn't have similar technology may not work very well.

Long before feedback detectors/busters, etc, I discovered ....maybe encountered is more accurate - something, on a gig. I'd built my PA speakers; EV used to have plans for a 12" Thiele cab. I used an EVM12L and I mounted Gollehan horns on top. Don't recall the crossovers. 
      I did a solo wedding gig in a small and very crowded room. The only speaker was right behind my head (with the horn above). I was using an EV RE-20 mic, which I loved (and miss). Anyway, it was very noisy and hot in the room. I dropped my pick and bent over to fetch it (tortoise shells were still legal then) and then through, "oh crap, it'll feedback!" But it didn't and my PA volume was "up" to compete with the gang!
     I "decided" the reason it didn't feedback was because the of the lack of spikes/smoothness of the mic and the speaker. So, there may be other ways/reasons that allow the PA behind you.
Michael

The Bose L1 system is based "loosely" around line array speaker theory where multiple speakers stacked vertically propagate a cylindrical energy pattern. The reason for reduced feedback is simply due to the fact that the microphone hears only an average of the total energy emitted by the system. There is no clever technology involved, just basic physics, though to operate as a theoretical true line array, a system must be cleverly engineered.
There is a great deal of information to be found relating to line array principles on the internet. Just google line array.
Many manufacturers are now bringing out small systems suitable for small stage use based "loosely" on the theory. Not true line array, but effective.

Tough to say whether your system can do this or not without knowing lots of other things - most importantly, how loud you're playing, etc.  Lots of factors go into whether your system can duplicate this or not.  If you're looking to see if your system can perform similarly, try:
- position the speakers as much to the side as possible to minimize how much speaker output is hitting your mics
- angle the speakers so they're not pointing directly into your mics
- not sure what type of mics you're using, however some mics are far better at handling feedback than others - something with high gain before feedback and low non-axial pickup would be better I'd think.
- play around a bit with your preamp gain on the mic.  Obviously the hotter the pre amp gain is set, the greater the chance for feedback.