Snake/Scorpio and Rooster/Sagittarius come in at 82-87%, a fully cross pairing with a surprisingly elegant fit: the most private, possessive sign in the book meets the one sign constitutionally incapable of telling a lie.
Snake/Scorpio wants what is mine to stay mine forever and struggles to open up to just anyone. Rooster/Sagittarius, honest to the bone and armed with incurable optimism, is the rare partner whose loyalty never needs checking. That transparency disarms the Snake's suspicion before it curdles, and the Snake's depth gives the cheerful Rooster real ballast.
Rooster/Sagittarius says everything, unable even to make a lie sound like one; Snake/Scorpio says little and remembers all of it. The balance works: the Rooster fills the silence honestly, and the Snake never has to wonder.
Friction flares if the Rooster's blunt truths hit the Snake's pride, since forgiveness is not the Snake's strong suit and revenge plots come naturally. The Rooster's open-handed charity to strangers can also prick a possessive nerve.
Rooster/Sagittarius teaches Snake/Scorpio that transparency costs less than vigilance and that not every slight needs a reckoning. Snake/Scorpio teaches the Rooster discretion, the difference between honesty and broadcasting.
At 82-87%, Snake/Scorpio and Rooster/Sagittarius show strong compatibility: total honesty answering total possessiveness, an odd bargain that suits both signs remarkably well.