Retire "directly away"

[hazelbark]

Of all the things to take from the other FOG rules, why use this language without clarifying it.
p 63 first sentence of "retiring units"

Retire "directly away from the enemy causing them to retreat"

So how is this measured?

1 Straight from center to center of units?
2 Away at a 90 degree angle from the causing units front edge?
3 or many of the other ways players can come up with.

It would be great to solve this with a FAQ or errata additon to glossary for "retire away"