To obtain the values for the "ShipSize" column, you need to put the following line into your sfc.ini file, at the end of the "3D" section.
WriteOutModelSizFile=0
Change the 0 to a 1, and then load the game up, and go into single player
Once you click the "single player" option, the game will appear to freeze, it hasn't, it is in fact evaluating the size of every model that is in the Models folder. Anything (except Space & Asteroids I think) which has a Model, it will evaluate. It will output the results to "model.siz" which you can find in the Models directory.
Inside the file, you need to multiply the value provided for the model by 100, and then that is what goes into the Core file.
As a bonus tip, you can use this to check the size of your model to it's break model. They should be exactly the same (or very close anyway).
This is all according to either the Beta Test Team, and/or Pelican; I apologize for lack of origination clairity.
This doesnt just affect the shield rings, but the size of the ship as well....
I DID NOT multiply by 100, and kept wondering for the life of me why my ship was super close-up all the time... if you want, do as I did, it was actually kind of neat!