Well, break this down.
The 186 is only 5cm different from a 191. The only thing that could add with length is a possibly longer turn radius which it doesn't need, given that it's elliptical to begin with.
Even if the rocker length were the same, that would only add about 2.5cm of contact length in the tip and 2.5cm in the tail, which really wouldn't be any better.
The Jeffery is an all-mtn jib machine. Jib. I think the shorter length certainly keeps unnecessary weight out of the tips and tails.
Basically, making it longer would move it out of the niche it occupies. However, check back next year to see the thing Tanaka is cooking up in AK.