XamDataChart common XAxis autoscaling increment size

I am using the 2016.1 XamDataChart with the ImmediateLineSeries configuration (this uses the writable bitmap to speed up redraws for complex data). 

I am adding points to the plot data collection in real time, and wish to make this act like a stripchart that displays the last 200 points - but also allow stopping and zooming to look at any of the data that has been collected sofar. 

I found that as points are added to the collection and the ActualMaximumValue is hit, the collection is resized and the display rescales to show the new data + some extra space.  The amount of the resize depends on the existing size of the collection, and appears to be about a 10% increase each time. 

Rather than a percentage increment, what I would like is to use a fixed (say 200 points) increment on each resize (which makes the stripchart work great), but I cannot find any way to get access to do this.  Any suggestions on how to proceed here?