UI - Pixel perfect pattern overlay

I'm trying to overlay a series of UI images with a small dot or grid pattern. I'm using the image component set to "Tiled" and and Aspect Ratio Fitter to keep the pattern (8 by 8 pixel blocks) quadratic.

The pattern seems to repeat correctly across my canvas which has a size of 1920 x 1080, but although the pattern texture is set to point filtering, the individual pixel squares appear to be anti-aliased or somehow blurred in the build.

I've played around with setting the Canvas to pixel perfect and also using a Sprite Shader/Material with Pixel Snap turned on. It changes the appearance but neither setting gives me a true pixel grid.

How do I create a pixel perfect grid overlay?

Grid pattern in build:

Grid pattern in editor: