Although OPs post is slightly confusing, and claims to show the 'secret hidden fare cost', his point can be summed up as thus:
Actual fees and taxes vary
Avios rate varies for peak & off-peak
RFS fee is £17.50
Therefore the 'value' of the Avios you spend varies.
I don't think this is any great surprise. The whole idea of the RFS is that it provides a standardised cost for European redemptions, and so there's bound to be routes where you're getting better value than others.
Incidentally, this can become more interesting when booking single flights into LON, where the fee is often lower than £17.50...