Another Rohloff-Schlumpf HSD combo on a 20" back wheel here.
The aim when deciding on the gears for my new trike 15 years ago was to have a range 10"-130".
The Rohloff-HSD combo let me do this, 30t chainring and 16t sprocket.
It was fine on tour but the shift into overdrive was only around 14 mph, to low for around town.
So I fitted a 13t sprocket, the shift into overdrive was now around 20mph but I'd lost the 2 lowest gears.
Then I had a brain wave... Twin chainrings and a single sprocket would fix the issue.
The spider on the HSD is 130mm, so smallest chainring is 38t.
Luckily the largest sprocket on the Rohloff is 21t, so I could keep my 1.8:1 chainring/sprocket ratio for the 10" bottom gear.
I know that ratio is not recommended but it's worked for 15 years/50k miles, but go that low at your own risk.
Now 3 gears up is 1.446x, so 38 x 1.446 = 55.7.
The 56t chainring doesn't work with the chainguard, chain jams against it when shifting, so fitted the 55t.
I spinout at 50 mph, done it a couple of times now, but tend to stop pedalling at around 45 mph.
It's "fun" pedalling slowly downhill at 40 mph ....