Units 'replaced' in the fight

[lowroller]

The rules on page 51 are perfectly clear what happens if the currently fighting unit is replaced by a fresh unit moving in from behind - the original unit pulls back to just behind the replacing unit.
However, if the enemy is attacked by a fresh unit from the flank, what happens to the original unit? It has to break contact, as the game stipulates one unit per side in the fight. So how far?  A minimal distance, just to show they are not involved? Or a standard morale result 'fall back'? (Which could be far more than the simpler example, so I doubt that is the intent).

[Leman (Andy)]

I clearly don't belong to the school of over-thinkers. No idea at the moment. I'm sure Martin will address the problem for you.

[lowroller]

I can't believe I missed it until now - I am usually a very thorough reader of rules!