I've tapped trees as small as 5-6" but only if they are designated for removal (and only on my property, I don't have permission to remove trees on my leases). Since the tap just feeds into my tubing, I can't comment on how much I got, but my guess is that the flow was OK but having a smaller crown the sugar was likely low.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.