Well I'll be hornswoggled. All along I've been operating under the assumption they've gotta be within 3 or 4 hexes of each other. As the game guide sez:
"Some units (especially infantry) have no radios and must keep voice contact, this is only reliable to 3 or 4 hexes (200 metres). A common fault many players have is to spread their units in a platoon formation kilometres apart, they are then out of command control, and if they get a reverse, they will then tend to run away a lot. Therefore, keep your leaders closed up to the men as much as is possible,"
Learn something new almost every day with this fascinating game. Thanks for the clarification!
Remember there is a difference between "CAN rally within 5 to 10 hexes" and "only RELIABLE to 3 or 4 hexes"- both statements are true!
I myself have found that as far as rallying is concerned, regardless of whether or not a unit has a radio or whether it is or isn't within LOS of the unit to be rallied, a unit can only give a rally to another unit within 5 hexes or less. Any more than 5 hexes and it won't happen.