Well, I can tell you what the rules say…
…but I cannot tell you how some players choose to interpret those rules.
It’s all described in Moving Into Contact on page 9.
At the end of the movement phase, one side or the other must be:-
(a) in full mutual front-edge contact
(sliding so corners touch), or
(b) in front-edge to side-edge contact
(with front corners touching), or
(c) in full front-edge to rear-edge contact
(with corners touching), or
(d) with no enemy in contact to its front, and in an overlap position (see p.10).
If this is not possible
(due to a lack of movement), the move does not happen.
(see figure 10)So then, who does the conforming?
This is fully described in the next paragraph:-
A single element must conform when contacted by a moving group,
unless the single element is entirely in Rough or Bad Going.
Otherwise the moving troops must do the conforming.
(There then follows a subsection describing if there is a lack of space)This is then further clarified in more detail by the FAQ:-
Q: I am moving a line of Spears as a group. I can just barely contact the rear of a single enemy Cav element in
good going with the
corner of my Spear line. Does it have to conform?
A: No. You must stop short. To force the Cav to conform
you must contact it with your front edge in most cases...
not your corner. The only exception is when contact is prevented by part-element spacing between enemy
elements or physically blocked by elements, terrain or a table edge.
Q: I am moving a line of Spears as a group. I can just barely contact the
rear corner of a single enemy Cav
element in good going with my front. Does it have to conform?
A: Yes. A group contacting a single element in good going with its
front edge forces the enemy element to conform.
In this case, the Cav will conform on contact to having its flank or rear (whichever requires the least movement)
in contact with the Spear. The Cav will then turn to face after the movement phase.