The 'Minimum Category' value, like Carl says, is calculated as an average of 95% of your 3 best 20-minute results over the last 90 days.
The 'FTP' itself: Not sure, actually. Tried to crack the algorithm but nothing seems to fit. In my case, the 20-minute power in those three races was 197, 204 & 208, giving an average of 203 (100%) or 193 (95%), but the displayed 'FTP' is 198 - smack down the middle of the two.
It might be that it's just a smaller sample. For example, I only did 3 races so far but none of them required a sprint finish - on all occasions I was in no man's land. As a result my 15s effort is the best 15s I just did in one of those races without an intentional sprint. You might have done, say, 200 races, all of them over 20 minutes but only half had a 15s sprint, making the sample size half as big and less accurate.