Tiled background stops tiling at large sizes

I'm following this https://www.youtube.com/watch?v=yuPpQoBJvvk&feature=emb_title tutorial on how to create a simple tiled background for a 2d game, and it's worked except that when I expand my image beyond a certain size in the sprite renderer it suddenly stops being a repeated tiled image and turns into a very large scaled up version of the original image. As best I can tell it's based on increasing size beyond a certain total area, not the height or width individually.

I can just create multiple smaller instances of the background if I have to but I was wondering if there's a size limit to tiling a sprite or something else that is messing me up?

Thanks for any help.