How do you baseline branch-to-VNet latency? The built-in metrics keep lying to me

Ok this one had me going for a good week. Two of our branch sites were dragging getting to the Azure stuff and i was dead sure it was the last mile, so i swapped both circuits but nothing changed, which is when it clicked that it wasn't the last mile at all. The traffic was hairpinning out through some region half a country away before it even reached the vnet.

The Azure latency graphs looked fine the whole time which is what threw me, they measure from inside their own edge not from my branch. Once I started probing hop by hop from each site to the actual workload the real picture showed up, embarrassing how far off id been.

How are you all properly baselining this? trusting the expressroute and peering metrics or running your own probes from each site. Mine and Azures disagree enough that I stopped trusting the built-in ones.