I found that the magnets, once stuck in a row, don't matter which way is north or south, they will work.
I set them to be roughly level with the track top - with code 75, they glue to the foam underlay and are pretty much at railheight.
That could well work with code100, otherwise a little .25 shim might be needed.
Once at track level, they work perfectly will with kadees once they are set correctly, I had a few mounted in the craven NEM socket, which is too high anyway, once I glued the kadee underneath, it worked perfectly.
I've since painted them muddy track colour and they are basically invisible! Will give them a lick of yellow so I can remember where to stop trains!
Just ordered another big batch myself - considering they work out a few pence each, and a kadee uncoupler is 5-6 pounds, plus is mahooosive!