To what extent is party unity and personalization a product of electoral institutions? Several studies in institutional research on elite behavior argue that party lists controlled by party leaders promote party unity while party lists controlled by district voters (i.e. open party lists) promote personalization. However, it has been difficult for previous studies to rule out confounding factors, because their analyses rely on observational comparisons between countries to get at variation in the relevant institutions. This paper uses a unique dataset of Danish local elections where electoral institutions differ between and within parties, districts, and over time. We couple this with a subnational Voting Advice Application in Denmark, where almost the full universe of potential candidates reported their positions on a large number of political issues. With this improved design we expect to find that institutions matter for elite behavior, but also that these effects are conditional on party leader incentives to pursue broad-appeal strategies. This interaction between party leader incentives and the effect of institutional design has not been explored in prior research.