Unlike normal tabletop rules, you do not pay any buy points for command units in SP.
Therefore the best formations in SP would be as many sections of 2, or even singletons as you can get without running into the maximum formations limit.
The Russian 10 tank companies are there only to provide the low-experience situation around Barbarossa. They are designed precisely to make command and control bad, especially WRT casualties, and the need to keep all 10 tanks withing 5 hexes of "father" if you want to ensure contact.
USA and German 5 tank platoons actually did not operate as "lumps", but usually a 3 tank heavy section and a 2 tank light section, or 2 2s and a roving platoon command. 4 tank platoons generally operate as 2 sections of 2 in close proximity. But SP does not have a section able to be placed under a platoon's command.
3 tank platoons do not tend to operate in sub-sections. They do have command benefits though IRL.
This tanknet thread should be of interest:
http://208.84.116.223/forums/index.php?showtopic=27105
Cheers
Andy