Well how else would you make some penalties to long distance wars? Only up the cost of it? Realms with big money would clearly have huge advantages then over less richer realms.
WIth all due respect, that's a bit nonsensical.
Of course rich realms do, and should, have some advantage. That advantage should obviously diminish with size.
IMHO, I like the idea of making "mercenary" create a "fixed morale drop," but have escalating price with distance from home.
So you might be able to preserve your morale at 70% or so... and be paying 4x or 5x as much per day for your unit. And maybe still an increased battle-penalty (mercs don't actually like fighting, obviously, especially far from home).
Which means that a realm would be able, for a long-range campaign, to field 1/4 or 1/5 its normal CS. It would deteriorate rapidly after battles and be fiendishly expensive to maintain, and no realm would be able to field a massive army of conquest at a very long range. We'd be seeing long-range armies of 3-5k CS. Which seems totally plausible. A large coalition of several big realms, which was able to work out lots of diplomatic hurdles, coordinate lots of different people and different interests, and agree upon a target, should, generally, have the capability to strike at it.
Realms should not be able to sit in the corner of the continent and yell insults at everyone else, then sit there smugly while vast armies desert in anti-war protests immediately after landfall.