On my '18 107 with a Stage I set-up the worst mileage that I ever got (doing math in my head) was approximately 25 MPG's, with the fuel warning light coming on at 125 miles!
This was freeway riding at 75 MPH with a "headwind".

The best that I ever got was (again doing math in my head) was approximately 37 MPG's and having 237 miles on the trip meter.
This was in Canada, mostly on two-lane roads at speeds between 50 to 65 MPH.

I've owned a lot of H-D's and with all of them, the best MPG's are done with keeping the tachometer under 3,000 RPM's and in a few instances, I've got as much as 58 MPG's (on two-wheelers of course).

Just a note about our bikes and trikes:
If you're concerned with "fuel range" on a tank of fuel and especially if and when you're riding in "rural areas" where gas stations are not plentiful, take the time when you're "filling" your tank to allow it to "burp" out the air and to fully fill your tank.
I even use the handlebars to "rock" my trike a bit and I discovered once that I got in an extra 4/10ths of a gallon of gas by doing this.
If your trike get's 32 MPG, that 4/10ths of a gallon of gas equates to approximately 13 MORE MILES per tank and could be the difference between making your next fuel stop or sittin' on the side of the road our of gas 13 miles SHORT of the gas station!

FWIW, for decades (since I one ran out of gas on my '69 BSA 750 Rocket III) I've kept a 5' piece of clear siphon hose rolled up in my tool kit.
You never know when U (or someone else) may need fuel