That is why I go for 7 kori, so I am using up 7 slots to gain 6 slots and only have to deal with a +4 RR to each. The extra income and retinue cap helps quite a bit once you are trying to field several generations worth of matchlock retinue and large ronin armies.
One thing I would like to see is the penalty per kori above the limit for a Clan Leader to drop to +1 or +2, so that it is still painful to have extra, but not something that will cause a civil war. This would enable you to carry a few extra kori for a while before you hand them out to your vassals. My idea is because you are asked by every vassal about once a month for the next Kukojin title and this would allow you to appease a few of them without carrying an insanely high RR.
On a second thought, perhaps the penalty should be a drop in tax level per kori over the limit for a clan leader. That way you do not benefit much from holding over the limit and it encourages giving the kori to a vassal, but does not discourage holding a few extra so that you have more to give out over time.