Yeah, I had pretty much reached the same conclusion.
Which is more generally described as:
If you have 2 accounts, Me@Provider1 and Myself@Provider2,
both with SpamCop Mailhosts configured on the same reporting account,
then SpamCop won't target Provider2 with reports when Spammer@Provider2 spams Me@Provider1.
Even more generally:
It is harmful to add a Mailhost config for a retail mailbox provider
to a SpamCop reporting account which has any other Mailhost config.