I was reading a scientific article and encountered the sentence 'Lack of A prevents the activation of B, which is primarily required for digestion, and later for the absorption of....', where A and B are some proteins.
What confused me was the usage 'primarily required'. I felt that 'required primarily' would be a better choice. I actually did not understand why I felt that. So I tried to find the difference between the two usages.
I did find some articles that used both expressions, but none that explained the difference, if there are any. Ngrams shows that both are used at similar rates even though 'primarily required' has been used slightly more in the recent years.
What I want to know is, do the two expressions convey different meanings? If so, what is it? Can someone please help me?