Form 12 Tax Relief on PRSA AVCs linked to Single Scheme

My Form 12 appears to me to be providing for more tax relief than allowed. As this is happening for more than one year it has me questioning my understanding of the tax relief to AVCs.

My understanding was that your age allowable relief % was applied to your gross income (or pay for USC) and then the total contribution to the single scheme (GPR & NPR) for the year was subtracted from this leaving the remaining amount being the cap to AVCs subject to tax relief.

However, when completing my Form 12, it populates my gross income and the amount of total net pay contributions relieved under the net pay arrangement correctly, I populate my NRE (same figure as gross income), but when I input a high figure in the AVC amount paid by me to see what the max would be in the auto updated 'Allowable AVC relief' field it is giving me a higher figure than what should be my gross salary at 25% (age bracket) - single scheme contributions.

Anyone able to work out how the Allowable AVC relief figure is arrived at? It's not a major difference but it's annoying me that I am getting a different figure as I had planned my monthly AVC contributions to work out to maximise the tax relief but now I'm slightly under each year.

Figures for each year are: