CE Shape Extruder - Z distance issue

Hi,
I haven't watched 100% of both tutes yes, as I'm pressed for time and it's an hour or so of video - can someone briefly tell me what the go is with the depth of the extruded layer being the same or similar no matter how close/far away the camera is?
I've got the project file downloaded with the tutorial and opened the "Text Simple" comp. I animated the camera over 5s to fly from extremely close to quite far away...
Far away, the text looks quite fat. The close you go, the thinner the extrusion is.
Is this normal, and if so, how does one counter it so that the text stays the same thickness? Do you have to animate depth and density?
Could you hook up a depth/density expression to the distance of the layer from the camera or is it not so proportional?

Just wondering, because if i want to fly through the text (a letter O for example) this could cause problems.

Thanks,
Scott.