Thanks. But what I want is to pay the fare difference for the DUB-LHR segment only, and not the combined DUB-LHR-JFK segments.

While that was (briefly) available, I ticked to upgrade the first segment, and leave the other 3 segments unaltered. But still got offered a price to upgrade the first TWO segments combined (from ET/WTP to CE/CW).

That’s the apparent “coupling” I want to split (in hope of getting a much smaller “fare difference).