Modern Dashboard - Sizing Widgets

I'm playing with modern dashboards for the first time - as I finally have a bit of breathing space to play. So I've long wanted to create a Top 10 specific to each client, but I hadn't been able to work out how in the old approach. 

So my first foray into MD is to do just that, and so far so good except a little sizing issue.

So I've created a Top 10 widget via hand built SWQL and it lists my max response times nicely but it defaults to only showing the first 8 - a la:

which has a nice little scroll bar. But if I then drag it out to show the entire 10 it gives me a sizeable blank area - a la 

And no matter what I do, I can't get the box just to stop after the 10... anyway of stopping this?