Layer Space Transforms and Size

Hi,

I have a 2D layer following a 3D layer using toComp in an expression, and its working really well. However, when the 3D layer gets closer to the camera, it appears as if its bigger, and I'd like the 2D layer's actual size to match the 3D layer's apparant size. Is it posible to do this in an expression? Thanks,

--Saib