Script or Query for Management Group Compliance Statistics

I've been trying to reproduce the Azure Portal Compliance statistics for a Management Group in a

 PowerShell script or Resource Graph query without much luck. What I'd like to do is reproduce the numbers like compliance percentage, number of compliant / non-compliant resources, in the portal display. And run a daily script or query to track the numbers over time. (Without doing screen shots every day.)

Just to be clear, I've attached a screenshot of a compliance screen for management group TEST1. I want to automate calculation of the Overall Resource Compliance (46%, 317 out of 692), and the policies/initiatives compliance state and resource compliance percentages at the bottom of the screen. I'm only interested in the resource compliance percentages below a threshold like 90% in order to help guide our remediation efforts. 

I've found several scripts and resource graph queries online but none seem to address management group scope. And even the ones that produce numbers for subscription scope don't seem to match the portal numbers. 

Has anyone successfully reproduced the portal MG compliance numbers with a script or quiery? Or, is it possible to obtain the logic behind the portals' MG scope compliance code? Seems like we should be able to reproduce the numbers shown by the console. 

Thanks.