GIMP :: Calculate Points For Curve Bend?

I have a small company doing designs onto mugs, steins, pints, etc. I recently added the ability to do custom photo designs, so now I'm trying to perfect the image curvature for my pint glasses and coming up against a problem.

So - with a pint glass, in order to put a design on it you actually have to curve the image. I'm following this tutorial here - [URL] where he shows how to use GIMP to curve a photo to insert into a tumbler.

I am doing the same process except my dimensions/numbers are different. I need to be able to create the appropriate .points file for my pint glasses but if I use the one he created, my image will be off since the pints don't have the same dimensions as the tumbler he did the tutorial for.

SO - all this to say - how the heck do I calculate what values to put in the points file? For example, on this particular project I need to make an image to be curved up 5/8" on the bottom and 3/4" on the top. He used .25" and .3125" so if I use his file, my designs won't be right.