I had heard this, too, and honestly didn't believe it - I assumed that if it happened, it was due to perhaps gaining weight or muscle, but not just "being on T".
It's hard to tell with mine - I did have to buy a larger ring size (been on T for 18 months) the last ring I bought, but sometimes I think that the change in size may be due to the weather being either hot or cold so not really being due to T.