Here are dome shape and opening size calculations I have made that might be helpful. I don't think it rocket science other than not making your opening so small you cannot get your favorite peel or pan into it (which I did on my first oven because I was trying to optimize it for bread), and so large that you loose heat too fast. If you stay roughly within these guidelines you should be safe:
Oven Sizes
Interior D Interior H Opening W Opening H Volume Ratio
Casa90 35.4 16.5 18.5 9.8 0.31
Casa100 39.3 15.3 18.9 11.8 0.37
Casa110 43.2 15.3 18.9 11.8 0.34
Premio90 35.4 19.7 18.9 12.2 0.33
Premio100 39.3 19.7 18.9 12.6 0.31
Premio110 43.2 19.7 18.9 12.6 0.28
To get an idea of curve difference, you could look at the prefab data sheets on our site. There are graphics that show the curvature difference between the two style. In fact, our producer calls their low style (our Casa) "Volta Bassa" or low vault.
James