I am having trouble figuring out how to change the
public override float GetHeightForRow (UITableView tableView, NSIndexPath indexPath)
It looks like you are doing it correctly by overriding GetHeightForRow, but if its not changing it I'd suggest checking your ViewDidLoad method on the controller to make sure it's setting the tableview source to your custom tableSource class.
For example, in
_tableview.Source = new TableSource();