For the tags to work they need to be close to your aura. They are programmed to so a few feet away. So, pocket or carrying will work as it is actively influencing your aura. Think of your aura as some part of you that overextends, as long as the field connects with the aura you’re all good.
There’s some belief and reasonable theories that closer to the heart might allow for the fields to acclimate better (as in faster), which is also why many seem to prefer carrying the pendant. However, there are circumstances where it is not handy to do so, imagine that you go for a run… So, many place them in the pockets and they still work.
The left side might allow for better engravement of the information, especially if supported by other fields/sigils/servitors on the right, I believe.
You may find also experiences with the tag there. I will tag here @Septimus as he has the tag and certainly has more directed experience than I.
Also, refer to:
https://forum.enlightenedstates.com/t/eternity-redux-dog-tag/1618/26
LASTLY BUT OF UTMOST IMPORTANCE, regardless of what happens: Please do not try to meddle with the field IT WILL GROW 
Read this https://forum.enlightenedstates.com/t/why-you-should-stop-boosting-fields/4432