Hey J. Going to the 70's will add about 3/4 of an inch to the sidewall height. That will close the well gap by that much. Note that this would also raise your bird by the same.
The 70 refers to 70% of the first number, which is your tire width, sidewall to sidewall. So you are going from 60% of 205mm to 70% of 205mm for the sidewall. The difference of 20mm is about 3/4 of an inch.