I've considered a much wider rework of EW, but for now I intend to just update ECM/ECCM. With the addition of various impending missile changes, I don't want to change too much at once.
I was already leaning toward the general principle of the proposal above, which is that ECM should be a percentage modification to chance to hit (CTH), rather than an absolute reduction. I also like the principle of taking the difference between ECM and ECCM levels (let's call this EW Advantage or EWA) and using that as a single modifier. So ECM 3 vs ECCM 1 would be an EWA of 2.The question is the size of the modifier.
If we use the first option above, which is effectively CTH / (1 + EWA), then an EWA of 1 would be a 50% reduction and an EWA of 2 would be a 67% reduction. That seems too high.
The second proposal above is a more graduated change, using a new modifier called C. The proposed formula is (C * CTH) / (C + EWA).
If C = 2, then EWA 1 reduces the CTH by 33% and EWA 2 reduces CTH by 50%. However EWA 5 only reduces by 71% which doesn't seem enough.
If C = 3, then EWA 1 reduces the CTH by 25% and EWA 2 reduces CTH by 40%. EWA 5 reduces by 63%.
The above options assume that higher EWA has diminishing returns, so that each added point of EWA has a smaller impact on the chance to hit than the previous one.
A different approach is taking the concept of EWA and using a linear percentage reduction - 20% for example - rather the current linear absolute reduction. This is simple to understand and avoids the problem of a low chance to hit missing automatically with a relatively low EWA, although it does mean that an EWA of 5 is an automatic miss, which doesn't seem unreasonable; consider the Earth - Minbari war. This could be considered a nerf to ECM as it would have significantly less impact on current low CTH situations, although it would have more of an impact for high CTH to hit scenarios.
At the moment, the linear approach is my preferred option, although I am open to being convinced otherwise.