I have the same issues with my TCS but not with all the mags. Must be some tolerance issues with the polymer mags as some fit pretty well and others rock back and forth a lot. The feed problems drove me crazy as they were intermittent dependent on which mag was in the gun and if I was applying pressure to the mag from a bag. Using extenders exacerbated the problem by giving more length/leverage for the bag to push.
The tape does help, for me it was a patch or two on the front of the mag body just under the feed tower. It is not foolproof however, if you put excessive pressure into a bag they will still dip and misfeed.
I just acquired a barricade block from Area419 that should help keep some pressure off the mag bodies.
On a side note...
For the two worst mags (I actually pulled from the trash can) I have devised a way to modify the front feed lip area to allow you to adjust it's height to accommodate the different angle caused by the loose fit. I will use them for the first time in two matches this weekend. We'll see,