The 105 D is different from it's predecessor in that it covers the outside edge of the wall plate rather than sit inside of it with it's edges making contact with the teflon sheet. However, both covers are still being sold, the NCF version is about double the price of the non-NCF cover. So with the previous cover you use the teflon sheet, with the NCF cover you do not. I switched from non-NCF to NCF receptacle and cover and left the teflon sheet in place, it doesn't matter so much but with the new NCF cover it's just not being used for anything so it can be discarded.
Now, with the 105 D NCF sitting on the outside edge of the wall plate there is a small gap in between the cover and receptacle, the screw that attaches it to the receptacle can actually bend the cover as it is tightened and this has a small effect on the sound. I prefer to adjust the cover so there is a small amount of tension, maybe a half turn of the screw past where it makes contact.
I hope this is clear, it will probably make more sense once the parts are in-hand. Currently, all GTX NCF, wall plates and covers are not in-stock. More should be here in 2 weeks but I'd consider ordering now to make sure you get what you want as the shipment may sell out before it even gets here. This is common after the holidays and took a couple months to catch up last year. I do offer free burn-in, shipping, etc. so please let me know if I can help!