I really don't get your point.

Right now everyone has 30 witness votes. Where each witness vote is worth the full vests the account has. Let's denominate this as "x" vests.

If the account only voted 1 witness, this witness would also only get one vote worth x-mv, thus, he should vote 30 times since this way he is able to distribute 30 x-mv in votes.

If we restrict his power to 10 votes, he will be able to vote 10 x-mv in votes.
And if he splits this up, it's not worth it.
The total quantity the account is able to vote is 10 x-mv, or 20 x x/2-mv or 40 x x/4-mv, but the more the account splits it, the more difficult it will be to make the vote decide who is in the top 20.