Eloqua Subject Line Optimizer tool question

I'm hoping for some insights on the "secret sauce" of how the Subject Line Optimizer works. I've come across several situations where our email got a great open rate, however the SLO tool gave the subject line a "below average" score - and vice versa, our email received lackluster opens and the SLO tool gave the subject line and "above average" score.

Our AI has been enabled for over 10 months, so we've "fed" the tool a very large amount of subject lines so far. Anybody else come across this? I'd like to make a case for our marketing teams to utilize this tool, but i'm unsure of the reliability.