If I'm not mistaken, in the lineart, the chest section of the 1D does not have the indent (where the head sits) and the canopy extends further backward. In other words the section of the chest where the heat shield slides out is the same length (the canopy is extended the same distance as the indent is in the normal variants, so its just like they moved that part of the chest up but its the same size). So in reality it would be pretty much the same (the head would sit higher but the extended part of the canopy would be exposed the same amount as the 1S). I guess pics would help but I don't have any handy. Of course I could be mistaken but that's always how I interpreted the lengthening of the canopy.
Edit: I checked the lineart of 1D and 1A and it seems that the middle part of the chest is actually shorter on the 1D, so its not just shifted back. On the Yamato it's definitely the same size tho. Hmm.