If they didn't think the fee would be this high, they presumably thought what..... £50m? so they'd pay tubby £10m and net £40m.
£100m even after paying £20m is still net £80m.
What the 20% turns into in pound/euro value is irrelevant as every £1 the fee is higher than they may have expected, is 80p to Juve? The higher the fee, the better for them?
They're just playing hardball and we should tell them to call us when/if they're ready to accept our offer (and they'll pay agents fees as they're meant to). Or, they can try and plug their cash flow without the Pogba fee and we move onto another target..... fine by me.