Just spewing it out here:
I've been wanting to pare down the imperial side of MTU, keep things smaller all around. One way I'm doing this is maintaining the planetary sovereignty of those worlds not specifically classified as captive governments. This makes things a little more interesting. In the Fester subsector, the capital world - Fester - is your population A, Tech F world with the dominant hand - ships with the longest reach and highest capabilities. But there are several worlds within Fester's reach nearly as powerful: several tech E, one of which is a high pop world. These are worlds that can, and do, field their own navies. None of these worlds, then, can project too much of their power too far: it leaves them open to annexation by their powerful neighbors. They may have treaties with each other, but those treaties have to be backed by force. They may recognize the authority of the Emperor, but they won't willingly relinquish the power which allows them to influence him.
(I realize this'd be more clear with subsectors uploaded, but I can't really do that from work)
It's not a question of maintaining a front, or a blockade. There is no "front" in a spacewar: if your fleet is spread out enough to cover every approach, it will be destroyed piecemeal. Homefleets have to be powerful enough to withstand the assault of the full force of your strongest enemy: in almost every case, that means that if a world risks making a killing attack, it leaves the homeworld virtually undefended.
Now, the Naval bases that are scattered about the subsector and the neighboring subsectors: whose are they? In the Fester subsector, it's plain that one-on-one, Fester could take (and in the past, probably has taken) any of the other worlds in a fight. The Naval bases, at least here, are Imperial, and each probably has a fleet present for two purposes:
1) A waypoint for local patrols, particularly to keep tabs on the local threat/allies.
2) A support base for a strike fleet within range of those threat/allies.
Again, in Fester, all those bases can be assumed to be Festrian. In other subsectors, there will be local powers much more likely to maintain bases - though some may be Festrian as well. Fester is a pocket empire, but it's the biggest local one.
The strike fleet needn't be strong enough to take on a world's whole navy: but it needs to be powerful enough so that should that navy leave to cause mischief, it can ravage the undefended planet.
One way the Festrian empire is able to project power is through its vassal states: "It will please the Emperor that so-and-so will bring his fleet to such-and-such, and occupy it until such time as we see fit."
Now this model is shifting away from the "navy on the frontier" model I'd considered before: but for the players, the result is much the same: the Navy has bigger fish to fry than trade patrols, and it's not going to commit much more than a patrol cruiser to them. Worlds that can't afford their own navies might sometimes enjoy the protection of an imperial T ship, but more often than not they'll be dependent on the cooperation of armed merchanters for protection, and if they can't get that, then they're ripe for picking.
Patrol cruisers are actually pretty important IMTU, since the Imperium doesn't control the scout service: recon and "scouting" has to be done in-house. The T-ship's actually pretty good at that - though different navies might well use smaller ships for scout-courier duty.
What else of navies?
Fighters (and other small, fast craft) are the most efficient volume weapons platform: I'm going to have to kluge together some higher-tech fighter designs to make up for LBB2's lack of variety, but small craft in general (fighters, armed & up-computered ship's boats, pinnaces) will be very important to fleet operations. The high-tech navy will have a core of 1-2000 ton strike ships, each with a complement of carried craft: the need to have jump mobility will keep tonnage down.
The home fleet might have lower-jump carriers and battle wagons, but I suspect it actually doesn't really make sense in terms of gun-per-ton to do that: A 4000 ton ship doesn't have the range or speed of a pair of 2000 tonners, but carries the same armament; it might be less expensive in terms of drives, but expense isn't an issue. Perhaps some form of carrier/rider arrangement can be worthwhile - swarms of fighters can be very effective in LBB2 combat, and perhaps a 300 or 400 ton carried ship can be a useful compromise between the resilience of a starship and the speed of a fighter.
The thing that I really want to do with the Festrian Main is create more flexibility and variety in ship design and ship capabilities. Within most of human space a certain similarity of design will maintain - just how different is one sedan from another, one ship from another in a given culture?
Different ships of a similar class will be very different in design and layout, but the basic function will be the same. But different worlds should have different tactics, different strategies and different needs, and they'll need different classes of ship.
There should be more drastic differences when different cultures and alien species are involved. The Squillish, for instance: Their ships are slow (M1 or less) and only have jump when they are able to steal it from human ships. But they are able to launch considerably larger spreads of missiles than are compatible with traveller ships. The Pajarans have unusual jump capabilities in their ships, have mastered matter transference (they have transporters!) and they can disintegrate ships. (Though they generally don't.) As I go back through my subsector maps for the Festrian Main, I'll be looking for such opportunities.