Then just let them build a line and group them afterwards, they will keep the facing and the line, in MTW it was a bit annoying that they didn´t always keep the line. When the group was moving and you gave them another move order, they kept their relative positions, but not their heading, so insted of

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you could get

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if you know what I mean, it doesn´t happen in RTW anymore, that´s a positive thing about groups.