I wrote a sentence: "The model performance of other sites is similar to that as presented."
(1) Should I use "is"? I think "performance" is uncountable (refer in This question), so I use "is". But there are "other sites", should it use "are" instead?
(2) In this similar question, Mark Foskey says "...But you will definitely find that phrasing in the scientific literature...." in the end of his question. Does that mean both "performance" and "performances" are correct in the scientific literature? (I should have asked him directly, but I don't have enough reputation to "add a comment" to him)
(3) Is the expression "to that as presented" correct? What I want to say in a longer sentence is "The model performance of other sites is similar to the model performance of these sites that are presented in this paper." How can I simplify this sentence?