Sigma lenses almost invariably have AF issues, its a near impossible situation for them, which is why the dock is a necessary thing.
Consider that a Canon camera does not recognize a Sigma lens, so Sigma must tell the camera that it is actually a Canon lens. This is the source of a lot of the trouble, since the camera actually adjusts its operation based on which lens is installed.
Be thankful that you are able to adjust the lens to work well with a dock. The lens will probably work differently with a FF body.
The 70D with its live view s3nsor based phase detect eliminates all the front / rear focus hassle, and is a good thing for wide aperture lenses, it gives sharp focus at any distance, and it is consistent, which is a issue for all cameras up to now.