Agreed, if it was a high pressure the extra ducting would make sense, but not with a squirrel cage. You do however want to block off the front 6" of the grates, in front by the door so the air is pushed up thru the wood. In your case, a squirrel cage is the right blower to use.
Dave
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.