Scott's not fixated on Ramona here. He's fixated on the conversation.
There are two separate scripts being played out here. The first is the spoken exchange between Scott and the rest of his band-mates. The second is the unspoken one being had between Lisa and Ramona.
If Scott were focused on Ramona, he'd realize that what he was afraid of in >>106203798
was coming to pass. Ramona is noticing Lisa's visible attraction to Scott, and starting to wonder whether her feelings for him are reciprocated. But he doesn't notice any of this, and even initially misinterprets Ramona's later comments in >>106203895
, because he's focused on Steven, Kim, and Neil.
This is an interesting analysis, but I think you've got a couple things backwards here.