One thing about the modifier...when you use the -1 to all PD then a D has a base intercept number of 6.
So vrs a CMLT1 you are intercepting on a 2 (-3 for LT1 and -1 for CM). If we lower the value to -2 it would be a 3 which is what you would roll against without the -1 to all PD.
With the base of a 6 trying to stop Plasma Torpedoes and Plasma guns becomes "difficult." Both impose a -5; this gives a base of 1, which makes them nearly unstoppable. A 2 isn't much better, admittedly.