Here it's meant as a ratio of personal productivity, not a multiplier on the state of the codebase.

Yes. If you add two -2x programmers to the project, you decrease its productivity by 4 programmers. You don't multiply it by 4.

I started my professional career in a project where the previous developer had been given incentives per lines of code produced. Her approach was to do

  display_buffer[0] = 'H';
  display_buffer[1] = 'e';
  display_buffer[2] = 'l';
  display_buffer[3] = 'l';
  display_buffer[4] = 'o';

instead of having a print function and saying

  print('Hello');

This was on a 8-bit microcontroller with 64k program memory. And, surprise surprise, I, a humble CS student, was given a task to "implement software to control our new HW with memory paging mechanism, so that the software, which is larger than 64k, can be put on a 128k EEPROM, and then add a network management interface".

Well, having taken a look at the code we didn't have to do any paging; soon after deploying a print function we could put everything on one 64k page and the other 64k of program memory was just sitting empty.