just because the front floor is not wet does not mean it's not coming from the front for a leak.
remember, there is about 3/4" of asphalt on top of the floor. there are drain plugs in them, pull one out and look under. if there is water under there, you could have issues...

now, are you saying only the top of the floor mats are wet? that would make me think rear sunroof drain dripping directly on the mat.

open your hood, and verify the spring pockets are free of debris, and rust.
then under the spring pockets there are drains, and under that there are drains. verify all of them are clear. ALSO there are rubber grommets passing through the firewall, make sure none of them are missing.