Just a quick nudge back to the original question, what are the leadership ranks of the various units?
Batron=?
CruRon=?
According to
High Guard, the ranks between Captain (O6) and Fleet Admiral (O8) are:
Commodore (O7)
Captains command major ships. Fleet Admirals command numbered fleets. From that one might assume that junior commodores commanded CruRons and senior commodores commanded BatRons. Alternatively, commodores command CruRons and junior Fleet Admirals command BatRons.
However, background information refers to a number of rear and vice admirals. MT explained that by stating that rear admiral is an unofficial (or was it alternate?) form of Fleet Admiral and vice admiral for Sector Admiral. But the rear and vice admirals we've seen mentioned are all occupying positions below that of numbered fleet level (Vice Admiral Elphinstone, for instance, was commanding a task force of a couple of squadrons). So while a rear admiral might be a sub-species of Fleet Admiral, a vice admiral is unlikely to be a sub-species of Sector Admiral (Though I'm told it's concievable).
My preferred resolution would be to persuade Marc Miller to retcon in Rear Admiral, Vice Admiral, and Admiral as substantive ranks in the Imperial Navy. The IN really need more than 10 command levels (the first ten goes to fleets with lower-case 'f', i.e. several squadrons stationed in the same system, the equivalent of an army corps; after that you need subsector, sector, and Domain/Imperial levels). While the same rank can stretch over several command levels (there are a number of historical examples), I still think it's sloppy that a Fleet Admiral (O8) who commands all the forces in an entire subsector is the equivalent of a major general (army division level, the equivalent of a navy half-squadron).
A more messy solution is to say that the Fleet Admiral level is divided into three sections by seniority, and thar Rear Admiral is what a Fleet Admiral (Lower Third) is called, a Vice Admiral is a Fleet Admiral (Middle Third), and a Fleet Admiral is a FA (Upper Third). Of course, with such a setup, you'd expect fleet admirals to be the equivalent of a full general (O10) (Actually, the equivalent of an army marshal, but the army's O10 seems to extend to two command levels here

.)
If you do that, you'd have commodores for CruRons, rear admirals for BatRons, vice admirals for single fleets, and fleet admirals for numbered fleets.
Note that this could be the rule of thumb, not necessarily so rigid that you can't have non-standard ranks commanding a given unit once in a while -- especially not during and just after a war.
Hans