First of all, welcome to the Zapworks Forums!
It sounds like you are using Instant World Tracking, which traditionally relies on camera frames in order to keep consistency. Because of this, moving further away from the anchor can cause some displacement as the content is no longer in front of the user (or in the same camera frame it recognises at placement).
Instant world tracked projects are therefore better suited to experiences where content is in front of the user at all times (or at least as much as possible!).
That said, you could certainly try out the beta version of our improved world tracking for WebAR! You should find that this is a lot more stable when moving your device away and requires less points to anchor to - discover how to use this emerging technology here:
Have an awesome day,