I hope I understand you problem correctly, a bit difficult to get the visual.
Two things you didn't specify 1) how many results you expect to get per screen size 2) will subsequent requests result number be equal no matter what size? or also depend on the screen size? What i would suggest is to get the window size (I assume we are talking length) and see if you can get a number from that. For instance 600px/30=20. So if the user had a window height of 600px you would get 20 results. 800px would give you 23. is that too simplistic for what you're looking for?
