This data supports the Kropff and Treves 2008 model of grid cells, which I’ve discussed here: https://discourse.numenta.org/t/video-lecture-of-kropff-treves-2008
Edit to explain how that theory supports this:
In that theory: Grid cells are burdened with a “fatigue” which limits how long the cells can stay active for, and the fatigue takes time to wear off.
When you’re moving about in the world: time is distance.
Therefore the grid cell’s fatigue controls the size of their receptive fields, and controls the (characteristic) distance between two RFs.