Average AIO back compartment size

[SantaMonica]

Among all the different all-in-one brands, what is the average or smallest width of compartments on the back (sump) side? This would be the side-to-side distance.

I seem to see at least 3" on most models.

 

[VicD81]

Coralife 29G biocube

Chamber 1 = 3.75" X 3.5"
Chamber 2 = 9.25" X 3.5"
Chamber 3 = 6.75" X 3.5"