In the previous IK 2.0 beta, a new scale factor was used when in "measure by arm-span" mode. This new scale factor made a few avatars feel a bit off. But for a lot of us with somewhat un-proportional rigs or avatars with heels, it provided the best IK we've had in forever. It felt great to use and made it so we didn't have to do weird workarounds with playspace mover and the height setting. The new "measure by height" option didn't work for our avatars and made them feel like t-rexes. The two modes accommodated different avatars and usually one of the modes would work.
With the "scale by arm-span" scale factor being changed back, it makes those avatars (heeled and somewhat un-proportional ones) feel pretty bad. We now suddenly can't properly kneel or do poses relying on the back. Every time we want to bind in, we have to mess around with playspace mover/height adjustment to get it right. That gets really annoying to do after a while.
I believe a toggle between the two scale factors would be best and would allow more avatars to be close to "perfect" with the new IK. A more complicated setting to just allow us to adjust the scale factor value directly would also be nice, but it would require more dev time.
Just please let us change it. I don't want to go back to needing to use an external program (playspace mover) just to replicate what was already a thing in a previous build.