Just an example not actual number, put emphasize on the word:

Actually, according to my data, the chance of a regular mob turn into seadragon in 13-1(H) is 2.78%… more on that below…

I have the data:

With 792 flags, 13-1(N) give 34 seadragons while 13-1(H) give 44. 44/34 = 1.29 (29% more)

On average, there are 18 mobs on 13-1

That means, in 13-1(N), the probability of a mob turn into seadragon is:

34/(18×198) = 0.95%

In 13-1(H), the probability of a mob turn into seadragon is:

44/(18×88) = 2.78%

But what is important is number of seadragons per flag:

13-1(N): 0.043

13-1(H): 0.054