When considering what depth Back Box to use, the general rule is to use a 3.5" box for stations with 3 or more connectors. (This is a change from the previous standard of 3.5" boxes for 4 connector boxes.) This will be reflected in the standard drawings. An exception to this is Unison and DAS stations which have only one data wire.
Smaller stations may want 3.5" deep boxes if there are more than 2 cables pulled through. ETC Standard drawings will not reflect this, so make sure the deep boxes are specified in this situation.