Any chance you could share a packaged workbook?
Hard to answer without an example workbook or image, but a few suggestions:
1. Try using Tiled instead of Floating objects
2. Try changing the Fit (on the view, or in the drop down menu of the view on the dashboard) from Standard to Fit Height or Entire View etc.
3. Try driving your visualisation through the use of a dimension on the treemap view, instead of multiple views being sent to a dashboard, so that you get multiple rows (or columns) of treemaps within the same view
I am not sure how you are using the parameter you mention.