As far as making overlays bouncy, there are specific modifiers that can be attached to a movement, called easing functions. This won’t make your code move from left to right, but you could try out:
@overlay ONE SIZE FITS ALL shifts to 12 293 in 2 using easebounceout
There are some others listed in the overlays section of the guide, if you’re interested in those.
As far as the issue with the zoom, that’s unfortunately how episode’s zoom settings work. Since the point being defined for an overlay seems to be at that part of the overlay, you will have to move the overlay with a simultaneous command for the overlay to move to the new spot it will be to make it look as if the overlay has maintained the same center point.