The 6 speed BWR hub has a wider gap between gears than the BSR,
but the left gear shifter changes between a 13 & a 15 t cog on the BWR
to make a half step , ratio to fill in the gap.

and so combined, the BWR 3 by 2 has closer spaced ratios.. you don't have to shift the left lever
until later, and you decide the right lever chosen internal gear is a little too high or low..



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FWIW Sturmey Archer lists a narrow version of their current 5 speed hub to build up in a wheel.
It does offer 1 gear lower .63:1 , to the 3 speed, gear set.. as well as 1 higher above the 3rd ratio..
3/4, 4/3 the regular 3 speed ratios , for 1st & 3rd.