In relation to this, I remember (i think from reading Polybius), that successor armies often weren't so much one straight line of phalangites, but more a line with joints. IIRC it was in the Magnesia description (could be wrong here though, it's been some time...), that e.g. some elephants were placed in between sections of the phalanx as well as on the flanks. Same with missile troops and mobile inf.
Now, was this common for successor armies or was it a rather innovative (and failing) approach, possibly developed on macedonians vs. romans experiences?