It will boil hardest at the top of the ramp. How much space did you leave between the bricks and the bottom of the flues? What size stack?
On my 3x8 raised flue I have 1/2" between the brick and the bottom of the flues, that forces the extreme heat into the flues. When boiling at first the top of the ramp will boil hardest, but if you fire it right the rest will boil hard too, just not quite as hard as the top of the ramp.
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.