Your’re right - Panel2 has no way of knowing whether power is coming from grid or solar and the mix between them, So Panel2 stuff should be correct. The problem is that Panel1’s monitor has a fixed calculation to treat IPanel1 + Isolar as Itot1 (correct), and IPanel1 when negative as To Grid, and when Positive as From Grid (wrong). The real from and to grid needs to be done by combining Ipanel1 and Ipanel2.
ps: I finally drew out the setup and there are really two nodes because there is a measurement between Isolar and Itot1. The orange rectangles are the CTs and the values in red are the ones that are calculated in relative by Sense.