As North Sea revenues have declined, the scale of the deficit gap has increased (revealing more of the onshore deficit gap)
North Sea revenues (~90% of which are allocated to Scotland) mean the actual deficit gap between Scotland and the UK is of course less than the onshore deficit gap - but as North Sea revenues have declined, the persistent onshore revenue gap has been increasingly "revealed".
As we have already seen, most of the bounce in North Sea revenues in the last few years has been due to the controversial Energy Profits Levy.