You can't do a convertible loan without both sides getting the valuation agreed.
(hence due diligence by FPP). I think that the agreed valuation for the shares will price us at somewhere around £40-45m. That's Donald's 'Championship valuation' and if they were coming on board after promotion, that would seem reasonable.
If that is the valuation, FPP investing £9m would roughly equate to around 20-25% of the club if converted. This is likely to avoid the 30% rule which forces them to make an offer at the same valuation for all of the other shares without the possibility to negotiate on price. Instead, they'd 'do a bit more' as Donald said, and get more equity from the next tranche of money when we got promoted again, which would prompt a full scale takeover.
So assuming that all of the above was done to the same level in the Premier League, the minimum at Sheff Utd level (£100m valuation) would be around £20m-£25m, but more likely around £50m to acquire 25% of a bottom feeding PL club like say, Palace.