Well I got a very speedy response from Sean at Lightning Vapes over the weekend and the replacement grommets are here courtesy of the USPS…
They mic'd out at somewhat over the 3.5 spec for thickness raising a bit of concern; however, so did the worn crusty factory insulators I was replacing. The fit was as good or better than factory. In fact they more resemble the post 2.2Ω head grommet in density and pliability than the originals. There was a slight improvement. Perhaps in heat resistance as well since I've not experienced burns in the material with 2.2Ω heads and later. It couldn't possibly be my technique has improved
that much in the past few months. So I speculate to suspect there was a change in composition.
The later iteration of grommets from Kanger have proven to me to be consistently a bit firmer, easier to insert and better fitting the assembly. Those shown here supplied by Lightning Vapes appear to match that specification exactly. Holding their form better than the originally furnished grommets they should likewise not bulge as much. At times such deformation inhibited airflow in Kanger tanks when the grommet was pressed into the assembly too tightly.
I'll try to come back with final impressions as I have more of these in operation. However, use with confidence.
Good luck!