Realistically, to use the minimum amount of ships without being suicidal, you need three things: Cargo space, an ASF screen, and a quick deployment force for when you are on the dirt before you unload the units carried as cargo. Points two and three can be carried by the same ship (for raids with surprise on their side, a heavy attack may need extra fighters) and all three can be condensed down into two dropships (A Conquistador and a Mammoth) if you go big enough. Which an LCT, by definition, would be capable of. There is after all no point in an offensive unit that can't offend.
But I doubt that LCT transportation is uniform. While a Merchant/Conquistador/Mammoth combination would be nice. I have no doubt that Invaders and Tramps (LCTs would love Tramps) would carry such units as well with the load spread over three lighter dropships. For Heavy assaults, where the enemy is known to have more than the usual number of fighters a Vengeance could be attached to the task force on a jumpship that has an extra collar such as a Star Lord or Monolith or by using only two big dropships.
I'd like to note that since it would be unlikely for another dropship to want to jump into a war zone, even if the military would let it, an LCT would likely have full use of every collar on their jumpship and it would make sense for that jumpship to be as efficient as possible. So in that regard I'd say that twin collar jumpships and twin transports would make up at least 50%.