Basically, I'm trying to to the opposite of Convert distance on MKMapView to distance for UIView.
I have a distance in UI View, and want to convert it to a distance of MK-MapView.
Why not just go to the documentation? You clearly haven't in this case.
If you had you would have found the method...
- (MKCoordinateRegion)convertRect:(CGRect)rect
toRegionFromView:(UIView *)view
Which is the one after the method in the linked question.
So just reverse the process from the linked question using this method.
BTW, to find the documentation for any class just put the class name into Google. The first link (most of the time) will be a link to the Apple documentation.