Thanks - I gave that a shot. This seems to work:
option channel 'auto'
option channels '149, 100, 36'
I had it as 132, 100, 36 first but it just seemed to fall back to non-DFS 36.
@mk24 My bad indeed, I checked again and see now 124 is the same block as 116. Tried the 132 block, no dice either.