In Scotland we don't have overhang seats on the AMS, or our version of AMS, so it's slightly different.
Split voting, which our German colleagues talked about, is called here “second vote” strategies. We just went through a Scottish Parliament election in May. The biggest party, the Scottish National Party, argued that both votes should be for the SNP, because that was in their interests. The Scottish Green Party—which doesn't stand in constituencies, but stands, apart from one or two places, only in the regional lists—would argue for the second vote to go to the Greens. So do some of the smaller parties, because they believe it is to their advantage. They tend to suggest to the electorate that they aren't going to win for their party in the regional list, they won't get any regional members, so they should vote for them because they are their second choice.