Before the mod the cobalt flux pad had obvious deadzones and required quite a bit of force to trigger.
After applying 4 copper strips to each main directional arrow it is night and day.
Below is not my video but a good idea of what to do.
https://www.youtube.com/watch?v=1Eber3JFSaA
I bought the copper tape as well but decided not to use it. I placed mine pretty much the same as above with most of them a little off center closer to the center panel. In practice you really don't hit the sides furthest away from each arrow, you usually hit hit closest to center pad.
Not too much trial and error on mine but ymmv. I went one arrow at a time in stepmania to verify no double taps were happening. Kinda curious how the bigger penny copper mod or big sensitivity modsteel plate is. If I ever mod my other cobalt flux I might try that.