Clamps being close should not be an issue if they are fully closed. But for some folks with panel space constraints, closing the panel can sometime push clamps open. That usually greatly reduces the measured current, but can also let in electromagnetic leakage / noise.
Based on your investigation so far, it looks like you might have a big long-term devices using power. Might you have another hidden heater somewhere. One of my favorite Sense stories here about old houses was one where a guy found a heater he didn’t even know he had.