One point worth mentioning about the SLDF Navy is that despite its size, it's still too small to provide each Army division with more than one or two WarShip escorts/transports on a permanent basis, not without drawing upon the numbered (ie. independent) fleets.
As per FM:SLDF, there's around 2250 WarShips in the active fleet, plus about 1000 more mothballed in the Reserve Fleet.
Most of the twenty numbered fleets have four squadrons, with a single fleet with just three, a pair with five and one with six, giving a total of 83 squadrons. Some squadron descriptions indicate that they have less than a full complement of WarShips, but there's also fleets with a command element seperate to the squadrons, in at least one case adding a whole additional division, so potentially 6 extra WarShips. Assuming the standard 18 WarShips per squadron, that would require 1494 WarShips, so allowing for short squadrons and the extras, a rough figure of 1450 could be used.
Assuming that there are indeed around 1450 WarShips in the numbered fleets, that leaves just 800 for the Garrison Fleet and those assigned to the transport squadrons. The Garrison Fleet is meant to supply two destroyers and/or a cruiser (one mention says some bases add the cruiser, while another implies the cruiser replaces the destroyers) to all or most of the bases (again unclear). With 450 divisions in the Army plus 520 bases, those 800 WarShips would be spread very thin indeed, and that's without considering the independent regiments.
Assuming instead that the numbered fleets normally only field two of their three divisions per squadron still requires 996 WarShips - drawing the rest from the reserve during wartime - and, with the scattering of extra vessels that are mentioned, that could easily be counted as a round 1000. Even then, the 450 WarShips that are freed up don't greatly improve the situation.
The likely answer is that the majority of divisions don't have permanent Warship escorts/transports and are only assigned them temporarily when they're on the move. That would thus explain how the 34th Royal BattleMech Division had 8 WarShips with it when it met its fate over Epsilon Indi during the Amaris Coup. Obviously the Army would be able to call upon the numbered fleets for support if the latter aren't off beating up the enemy's navy, and that could be a big "if".
It would be interesting to know whether any McKennas end up in the transport squadrons. It doesn't seem likely that they would be in either the garrison or reserve fleets, and with 280 McKennas and 83 squadrons in the numbered fleets, that could allow just over 3 per squadron if there was an even distribution. Some of the fleet and squadron descriptions mention 1 to 3 McKennas in a specific unit, and combined with the probability that few if any McKennas are assigned to the recon, survey/science and other lighter squadrons, that could mean that there are some line squadrons running around with six or more McKennas.