Hmmm...
Logismos appears to be just the mental faculty to "reason" things out in everyday life. I think of it as the decision-making ability of the mind. Logismos would be the colloquial name of the ability people use when someone has made a "reasonable" decision. I **think** it would equate to your "everyday" understanding of the word "logic" you've been using, Cassius .
I would concur with your last two paragraphs. I think Epicurus would include formal logic within the paideia (enculturation; instruction; indoctrination) he criticised, ex. "Set sail in your own little boat, free from all paideia."