How to increase Tag count

I recently read an IEEE research paper where the researchers were able to have one tag range with 7 anchors (without modifying the built-in firmware).

So, I was wondering if there is a method to have the tag receive ranging/distance data from more than 4 anchors (assuming they are all in range and Line of Sight). Can the anchors just send data and the tag receive the data from each anchor? Perhaps there is way to get ranging data per anchor in every superframe?

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