hanks Roger, ( i agree i'm wrong ..... sometimes

)
you're right , supported units from flank or rear can follow the counter charging even if they are out off the 4 UD, and artillery can also support melee if at effective or short range ( so lot of the time OUT off the 4 UD)
I re read the rules , i understand your issue....
Units can be in support position but not in groups.. ( I never see that before, but i agree it's possible) .Usually, units in support have the same facing.
For me, and i will ask tonight hervé, here is the resolution order..
1 / you must declare the charging units.
2/ you can charge in group (p42), and all units in the group can move at the same speed. (bonus included p42)
3/ if you charge in groups , you must end in groups at the end of the charge move.
4/ if you want to add more support (moral or by fire) who are not in group at the beginning of the charge, you must paid Extra PC.
5/ When the charging units arrived at 4 UD ( if started at 8UD or more) or when it have move half the distance ( if start lesser than 8UD) , one reacting units can counter charge or React.
6/ if counter charging , support units can follow the counter charging units ( in this case there is no mention for groups ... only support units

)
7/ defender and attacker can also add fire support if in range (effective or SK)
8/ DEFENDER CANNOT pay for moving other support to help in combat as he has got no PC.
Today, what i see in tournament is : you charge in group (defined p19) and if you want to add more support that are not part of this group you must pay extra PC (units from the same division) . And i think is the better solution. More clear.
I ask to hérve and i came back soon.