Which makes designating a second in command of the lance a good idea. Speaking of which, rather than Leftenant, Ensign or Lieutenant JG would make more sense, or possibly SGT Major. The majority of lances are led by Lieutenants.
The rank structure (which matters to us) that AtB can support goes like this:
LTJG
LTSG
Captain (company command)
Major (battalion command)
Colonel (regimental command)
The Founding Lance Leaders are all designated via LTSG tags, and the newer Lance Leaders which come in are designated by LTJG tags. I can't add a rank (Ensign), but my suggestion is going to be to bump all Lance Leaders up to LTSG at the end of the contract, and in the future reserve the LTJG tag for a lance XO from now on. That sound reasonable?
From a rules perspective (I never put this into the rules doc because I didn't ever anticipate it mattering; whoops), in the AtB campaign, for a character to act an an executive officer of the unit and contribute a Strategy/Tactics rating, they have to actually BE an officer. Hence, executive
officer. Which means that a sergeant can't contribute a S/T rating. This has technically been true for all the NPCs you've faced. Hat is totally correct that with the change to the AtB medical rules, suddenly having a chain of command inside your lance matters.