Stacked coils: yes, coils stacked, bumpy-side to bumpy-side.
Placement: Yes, I put the stacked coils right over the most painful spot.
Breaks: If you are using one of the pulse patterns that varies over time (such as Omni8, Alpha wave, SchumannX, basically any pattern that is NOT fixed frequency) then you should not really get used to (habituate to) the stimulation very quickly. If however you use one of the fixed frequency patterns “because that is what they did in the scientific paper”, then I suggest switching over to a non-fixed frequency. If the device seems to have become less effective over the course of a few days or weeks, then I would check the device function:
1- Use the hexagonal coil tester to make sure both coils are still functional.
2- When testing, move the wires around a bit to make sure the coils remain functional even when the wires are moved, to detect small breaks and shorts.
3- Make sure the battery is getting a full charge before each use, and swap with a freshly-charged battery every 3-4 hours
4- Counter-intuitively, if you are using one of the highest power settings, consider trying a slightly lower setting (9 or 10 instead of 14 or 15)
Weakness when walking: that might be due to a nerve pinch that is still a problem, even though the pain is reduced by PEMF. Some times it takes longer to fully resolve this kind of problem, so I would suggest continuing daily use, 6 to 8 hours per day or longer, and expect that this situation might take several more weeks to improve.