More a curiosity, but maybe a bug...

Clicking on individual Archeological Dig Sites shows me a different output level for Alien Artifacts for each one. And these are all sites that a full with workers who are working (75/75/75). Clicking on 5 different sites and I see 0.98 AA/min all the way up to 24.68 AA/min. Is this normal? Is it actually impacting production or just a visual glitch?