If missile launchers worked the way I'd like them to, it would go something like this:
A "Light" SRM launcher would have a range of 2/4/6, do 2 points of damage, fit in a 0.5 ton RWS, and be able to fire at 0-hex range.
A "Standard" SRM launcher would basically be a dual-tube "Light", have a range of 2/4/6, fit in a 1 ton RWS, inflict 1 heat, fire at 0-hex range, and roll on the 2 cluster table.
A "Heavy" SRM launcher would have a range of 3/6/9, do 2 points of damage, fit in a 1 ton RWS, inflict 1 heat, and be able to hit at 0-hex range unlike an SRM-2.
An MRM launcher would have a range of 4/8/12, do 1 point of damage, fire at 0-hex range, inflict 1 heat, and fit in a 1-ton RWS.
An LRM launcher would have a range of 5/10/15, do 1 point of damage, be unable to fire at 0-hex range (and in fact have a minimum range of 2 hexes), inflict 1 heat and fit in a 1-ton RWS.