Again, I see Sophia very differently. I don't think she was testing the MC, at least not in the sense that she was comparing him against preexisting objective criteria. I think she was simply poking him and noting how he responded because it gave her something to do. Like Sherlock Holmes, I suspect her brain craves stimulation; Holmes would resort to cocaine when business was slow, Sophia prefers to dose people with an unlicensed aphrodisiac.
IMHO, her making out with the MC has nothing to do with her feelings for him, she just wanted to figure why he wasn't getting off and fix that so she could get back to watching the Carnations who were testing the drug she actually cares about. She theorized Kathleen's handjob wasn't doing it for him, so she took action herself. If the MC starts kissing Sophia, she plays along until she gets the result she was looking for, at which point she seemed to lose all interest in him. Likewise, I see no banter in her quoted exchange with the MC in his living room. He said something she didn't understand so she asked for clarification.
This isn't to say that there can't be a more meaningful relationship between the MC and Sophia in the future; we're clearly going to be spending more time with her. But as of right now, I see nothing in her behavior that can't be explained as well (or better) by Sophia being every bit the disinterested henchwoman she appears to be at first glance. Your mileage clearly varies.