The LC+ smoke unit reservoir is a bit smaller than most Legacy or MTH smoke units. I typically use at least 20 drops to start an LC+ LC+ 2.0 smoke unit and then 10-15 drops when they slow down significantly.
Most of the MTH RK or Premier smoke units have the same size reservoir, they are the same smoke unit. The difference between diesel and steam are the length of the mounting posts. For some small locomotives, MTH does have a small single resistor smoke unit, that one has a much smaller reservoir and you need to be more mindful of overfilling it.
There are a handful of smaller smoke units in various Lionel offerings as well, I know the TMCC Mogul is one such locomotive with a small smoke unit.
The bottom line here is probably that you need to be somewhat aware of the characteristics of your specific locomotive and the size of the smoke unit.
