Hmmm... let me jump in for a moment. Can you have, for instance, four sub-frames combo'd together, with a couple being tandem and a couple being parallel? Or three frames with two being parallel and one being tandem? Then we'd have to define which of the first two the third one's tandem with, wouldn't we? And that would change the costing formula for having combo frames.
For instance, if I have Subframe 1 (12 PV), Subframe 2 (8 PV), and Subframe 3 (10 PV), and I combine 1 and 2 in a tandem combo, it costs 12+(8*.25), or 14. Now if I want to set up Subframe 3 in a parallel config, do I need to use the PV for Subframe 1 or 2 as the comparator? Or the combined combo PV for 1 & 2 put together?
Or, if I have an assault rifle with an underslung grenade launcher/flamethrower (a subframe with a tandem relationship to two subframes with a parallel relationship), how do I calculate that? Establish the parallel relationship first and then add in the tandem relationship?
I'm working on the Excel customizer again (finally!!) and this is presenting an interesting exercise in logic. One problem is forcing the user to account for what they are trying to do by combo'ing their weapons in the proper order.