Here's a thought.
Many people with long term mid drive experience don't like sprockets below 14T because they wear too fast.
But we really need these tiny gears to hit the top speed of the motor and a big chainring..
How about using an IGH to achieve the correct gearing and keep that short mount..
IGH will typically have a 19T or 21T sprocket..
This is good because it will raise your chainline and make it so you can fit a bigger sprocket and reduce that pedaling RPM.
Just read this article:
Mid Drive Kits, Dump the Derailleur and get an IGH?
Quick summary.. for the power level of the BBSHD they would recommend a 3 speed.. which sounds funny.. but people with BBSHDs end up using 2-3 gears anyway.. and we have that kind of power..
On my kit with a 48T front, 14T rear, and a 33% increase/decrease possible in the gearing, it'd work out like:
Gear 1 - 16mph
Gear 2 - 23.8 mph
Gear 3 - 31.6 mph
If i swap to a 50T front chainring then my top speed is 33.7mph which may be beyond the continuous limit of the motor.. so there's a lot of headroom to move the gearing now
Some people seem to have success with 8 speed IGH and high power drives. The Shimano Alfine 8 would be next on the list of IGH to consider, but is 3x the cost of a 3 speed IGH.