Scale your spot to one extreme and position it correctly.
Scale your spot to the other extreme and position it correctly.
Now, take the difference of the scales and divide that by the position difference.
Then this will give you the mulitplier for the scale.
Apply this multiplier to the position of your spot dependant on your spot scale.
Scale your spot to the other extreme and position it correctly.
Now, take the difference of the scales and divide that by the position difference.
Then this will give you the mulitplier for the scale.
Apply this multiplier to the position of your spot dependant on your spot scale.