Correction to my previous post. The gemara is referring to water vs dry matter, instead of water vs heavier liquids. Can’t fathom why I mis-learned the gemara like that. In any event, my kashya is still valid, and I did find over Pesach that the Ritva asks the kashya and he is madchik a teretz that indeed the calculations of 2:3 of liquid:dry is applicable in this unique case where the first two Amos are round and the remaining 3 are square.
Wondering if anyone had the opportunity to see a good teretz to this kashya. Thank you.