Project Online Portfolio Analysis - "cost limit" recalculation not in line with priority

Hello,

I've been setting up the portfolio analysis and doing some testing but the results are not as expected and Im not sure why...

I have set up the Driver Library and Driver Prioritisation then run the Portfolio Analysis - all good.

Then I change the Total Project Cost in the Cost Limits section and click re-calculate. For some reason it moves out projects that are a higher priority that would still fall within the constraint and brings in projects that cumulatively come well below the cost limit and even pushes out projects that could be included in that list whilst still meeting this limit.

How is this being analysed/prioritised? This doesn't seem correct to me.

Many thanks