Then it sounds like we are set up identically. The clamps at the bottom should show you net energy in and out of your inverter/backfeed, not just into your box.
When you first calibrate the Sense solar, you turn the inverter off so Sense can set the zero point for solar production. No production and no drain from inverter = 0. Once you have Sense operating, any flow back into the inverter from the grid shows as negative on the solar readings (I see small negatives at night - my inverter pulling from the grid to stay on in night mode). When it is positive you are seeing solely net production from the panels minus the any power going to the inverter.
If you think you see inverter usage showing up in your total consumption, I would contact support@sense.com.
ps: Some solar users used to see something that one called daytime dip, where total usage appeared to be connected to solar production, but it was a real error. Not sure what Sense did to fix, but I never saw it.