Ok heres my problem, if its even a problem, i have a innova scantool- can obd2 3130

i have a small exhaust leak from a warped header flange, so i was checking my spark advance, at warm idle, 823 rpms the scanner says -20 when i get in the gas... couldnt log at WOT because there was no where to do it but if i got on it a little it was saying -43

maybe i dont understand the scanner but why would i be running 20 degrees advance at idle.... or 20 degrees retard and retard worse as i get on it?

can someone help please?