The Bo had at least 1.5x higher fuel flow rate for the same cruise speed as the TB20 (as far as I could find out from the universally misleading sales data in this business)
I'm sure the A36 is significantly more thirsty than the TB20, and I agree with how difficult it is to get reliable comparisons, I am, though, a little surprised at your 1.5x figure.
FWIW, here's the actual fuel consumption I achieve with my A36, which has a normally aspirated, 300HP IO-550.
I generally fly shortish sectors (so climb fuel is a greater percentage), often 2 hours or less take-off to touch-down, fly with 'go reasonably fast' rather than 'go far' power settings, and generally cruise between FL080 and FL120.
In the cruise, I use 65% power with the mixture leaned to just slightly LOP. At those levels, 2400 rpm or more may be required at WOT - but 1900 rpm would be a more efficient way to operate the engine, saving approx 12HP in friction losses - and I get an average 165KTAS at just under 50 litres per hour.
And the bottom line? I average 62 - 64 litres of fuel per hour of flight time (take-off to touch down), inclusive of fuel used on the ground.
IO540, do those figures tend to substantiate your 1.5x?