I think I pretty much understand this sentence, it says that the human eye tends to prefer the upper center of a visual medium (for context, see the attached image). However, 観察しようとする 面の中央 poses a serious problem.
Concerning the human eye, the center of the surface (which) it makes an effort to observe,...
In this case, I used "観察しようとする" as an attribute to "面の中央", but I'm not sure if that's okay or not.
I also don't know whether そうである modifies the whole sentence or just the second half after より. The most literal translation of the whole sentence I can muster would be this:
Concerning the human eye, it seems that it looks a bit more natural at the upper direction (of the surface...) than at the center of the surface (which) it makes an effort to observe.
I put the brackets in to make clear to what I'm referring. I'm not sure if these reference points are correct in this sentence, that's why I feel unsure about my understanding of the whole sentence. I think that in the above standing version, そうである modifies the whole sentence, but I don't know if that's correct, as I already said.
For some reason I still feel notoriously insecure about the use of より... I apologize if I should've made a mistake on that one too, but it's hard for me to research it because the examples in my textbook were very bad and the texts only rarely bring up comparisons at all.
EDIT from 04-14-2017: I still have problems understanding the construction.
My problem mostly revolves around 面の中央 and its modifier 観察しようとする. Strictly speaking, that which the human eye "wants to observe" is not the page, but the center of the page here, right? After all, 面 is an attribute to 中央 here. I might overinterpret things now, but wouldn't this mean that the text basically says "The human eye doesn't observe just the center of the page, but only the part slightly above the center of the page"? What I want to say is that it sounds like the sentence gives us two negative statements about the human eye, because only perceiving the very center of a map isn't much better than just perceiving an area slightly above the center of a map. However, I feel like the sentence actually wants to say that the assumption that the human eye perceives the WHOLE map is wrong, because it only perceives the said area.
It seems that the human eye does naturally look at the area a little up from the center of the page it wants to observe
I mean, in this case it's relatively easy for me to just go with the option which makes more sense. But are there any other "hard" criteria in the syntax of this whole sentence or in the structure of the phrase 観察しようとする面の中央 which make it clear that A and not B is meant:
A: The center of the page it wants to observe
B: The page's center it wants to observe