Ole Boe (spécialiste des règles de "mur") vient de me répondre sur cette question de mur et de TEM.
En fait, il n'y a pas le choix entre le TEM du mur et le statut HD, mais entre le TEM du hex (si pas O.G.) ou la protection du mur (HD).
Il reconnaît que la règle n'est pas claire mais qu'un erratum va être donné dans ... le J6! :
The rule is far from clear, but its intention is that an AFV behind a wall, in a hex that has in-hex TEM may choose this in-hex TEM instead of being HD - just like other units may choose in-hex instead of wall TEM.
It cannot choose its wall TEM instead of being HD by that wall.
As said, the rule is far from clear, so I'm happy to say that one of the Journal 6 errata that I suggested and Perry accepted was to make clear that only in-hex TEM can be chosen instead of being HD. [/i]