New system:
You take five regions, put a Lord on each one, and have no problem keeping all 15 of your regions under control. Sure, you don't get full gold out of all of them, but you're still taking in some more gold than you were before you took them, plus the extra food. Over the next few weeks, you attract a few more nobles. When each of them joins, he gets to take an estate on one of the 10 short-staffed regions, which gives him an instant decent income, and increases the overall income of your realm. The general upward trend in the realm makes the old and new nobles alike feel good about its future, and new players who join are more likely to stick around, thus increasing its population and income further.
Example for the new system:
10 regions with 20 nobles: 100% coverage, 100 gold each region, 50 gold for each noble:1000 gold total for the realm
expand by 5 regions:15 regions with 20 nobles:
5 regions with 100% coverage, 100 gold each region, 50 gold for each noble:500 gold
10 regions with 50% coverage, 65 gold each (remember, additional penalties), 65 gold for each noble:650 gold
total for realm: 1150 gold
See? a 50% increase in regions should lead to a 15% increase in gold income. That number could be anywhere between 5% and 25%, of course, but it would be hard to find a scenario where expanding leads to less gold.
Actually, I can think of one--city/townsland/stronghold estate coverage. But you can probably free up one noble from each of those region types.
