AT fire in assault hexes

[cjsiam]

So My confusion was reading that combat in an Assault hex, was ASSAULT combat---either DF or AT fire.
That apparently is not the case (I will say I'm not the only one who labored under that perspective.....)

So it would seem that AT Fire can happen in an Assault hex...It is Not simultaneous....
Then, as a Defender, a unit which previously undertook AT fire can defend in Assault with their DF fire factor (this time simultaneous, unless they are first fire
  in which case they defend first)

This would mean that AT/Tanks NEVER get to use AT fire as their first fire---they must activate any AT Fire as a separate attack...First fire then is
EXCLUSIVELY a DF total on the Assault table....
So if a tank is adjacent to an entrenched AT gun....if it gets initiative, it moves in as assault---and suffers ONLY DF total, not AT fire at the tank...as it is Assault
I think that is how this then has to work out....
That means that with Extended Assault---that AT Gun needs to fire opportunity fire---which means if you're doing this as a german you send in an APC first...
because that precludes Opportunity fire on the Tanks (in the same activation)...that there is some combined arms....

Hmm...ok....someone clarify if I missed something.....