The rangeSize (and rangeDistance) for that matter are indeed missing in the MVC wrappers.
We've added them and they'll be available in the internal build that will be uploaded later today.
As a token of gratitude for your involvement your Telerik points have been updated.
Just a quick follow-up.
The rangeSize and rangeDistance settings are options of the scale. They were mistakenly documented as gauge options.
.Scale(scale => scale