Throw Ratio = Throw Distance / Image Width
Throw distance is measured from the front of the lens to the screen.
For images narrower than the projector's native aspect (e.g. 4:3 on a 16:10 projector) the throw ratio applies to the full projected width, so the image width is scaled up (4:3 on 16:10 = x1.2).
Lens offset (shift) is listed on each lens datasheet.