My brain's having real trouble parsing your post.
A UIGrid moves its child transforms by the cell size defined on the script. It does not account for screen size, Panel clipping area or anything like that. You have to define how many columns or rows you want.
If you put the grid inside a UIPanel, then you can define a clip range, wherein the content (UIGrid + children) will be able to Clip within the area defined on the UIPanel.
Does this help you?