Already tried that - was the first thing I did in fact when I initially saw this thread.
Sadly the channels available on US reg zone are 36-48 and 149-161.
Under channels 36-48 the USA-reg txpower is limited to 17dBm (vs 19dBm on UK reg zone), and UK reg zone only covers up to channel 140, and anything above channel 48 requires DFS, which is not supported by the A+ at all.
I've tried a few reg zones trying to find a zone that allows better output but I'm yet to find one.
Basically, with no DFS support, I can only *ever* use 36-48 in the UK. The UK reg domain on A+ only allows 19dBm on those channels. USA only allows 17dBm, Russia only 17dBm, and I've tried a few others - none I've tried to use give more txpower on channels 36-48.
If you've got any ideas on zones that might allow better txpower on 36-48, I'll give them a try but I don't hold out much hope....