Hi Michael...

>> But I think that makes sense to do the other behavior instead and stay attached to a touching curve, I think it should not be difficult for me to set that up, I will give that a try.

Interesting, to see the next progress....

>> If you have other curves touching on both sides of the arc, I guess I will just arbitrarily pick one of them to be the scaling origin.

Correct, this will work like constraint base software.
This will make edit 2D sketch in moi more easy and precise...

Thanks Michael..... :)