no you can't adjust the behavior - the only thing more important than charming is mezzing
we check for mez needs, then check for charm needs - we do this *many* times a second and we do this before we check any other enchanter specific combat related things (like assisting or dots/nukes etc).
we will try and re-charm a pet you had previously - if it is out of range or out of line of sight, we assume it is no longer a valid candidate.
I'd check with your tashthencharm in case it is getting hung up trying to do that