ACP / developer control percentage penalizes existing buildings?

I've done a number of Core and Shell models before, and always use the ACP calculator. However, something that I've noticed before but never understood is why the Revised Point threshold column is a single column and NOT separate revised thresholds for New and Existing. As an example: In a current project, I have a developer control percentage of 47%. It says that any savings over 13.8% gets you 6 pts. This is a nice drop from the 18% required for a non-ACP path to get 6 pts as a new construction project. However, the non-ACPT path for 6 pts requires a renovation project to have 14%. In other words, the ACP only lowers the 6 pt threshold from 14% to 13.8% for renovations. Why does this happen? Is it just something you have to live with for renovations? Or is there a way you can pro-rate this to be valid for existing building renovations? Thanks!