It's not very clear. On the face of it our map suggests we have more blocks than they do, but I don't really see how that can work.
We have have the East of the stadium, Watford have the West. The FA distribute amongst their members 7k tickets in the two ends and some of these have been returned to both clubs. I think it's unlikely that we have got the blocks on the half-way line as it would mean that Watford have not sold any seats in those and the FA have not done so either. I think the image maybe a bit misleading.
I do think we'll have more fans there than Watford though simply because there are a lot of seats allocated to neutrals for finals and some of these always work their way into fans hands eventually and we are more likely to get those than Watford.