Check the rules on what happens when toops in spontaneous advance pass through other troops.
Troops passed through by impetuous troops are mostly recoiled (excluding knights and other stuff like that). I'm not worried about that, but on elements pushed forward by non impetuous troops passing through them. In my example the first element of the passed through coulmn will be moved 2 cm forward, and this can mean that they can pin an enemy element that in other circunstances wouldn't be pinned.
[it] Having read more closely I see that "spontaneous" refers to interpenetrating elements that would *end in contact with enemy* so I surmise it means "advancing spontaneously". Fleeing and routing elements *can* contact enemy albeit in a very select set of circumstances.
If a passed-through element is required to recoil the element passing through will not usually displace the element further to its front because the recoiling, passed-through element has vacated the space required by the advancing element. I say "not usually" because differing base depths can upset the "space making" intention. In reference to your original diagram the 2nd rank Bd could recoil and still require the 1st rank Bd to move forward, just a bit, to leave room for the Ps.
Elements in an enemy TZ are permitted to move "directly towards the enemy exerting the TZ" [Pg32 Threat Zone Para 1 BP 5(c)]. If the opposing elements were lined up then the 1st rank Bd, displaced forward into or further into an enemy TZ, would not be doing anything that couldn't be done with PIPs**. "Directly toward" implies, to me, the requirement to pivot and/or shift to line up, ie not end oblique to the enemy element's front - otherwise why not simply state "towards". I presume EMTLU could be used to achieve this insofar as the displaced 1st rank Bd would be "moving in an enemy TZ"[Pg33].
** I suppose there could be a PIP saved if an irreg element is is at the front, oblique to the enemy front - it would be an extra PIP for the "not-straight-ahead" tactical move whereas the EMTLU would be PIP free. I suspect one would have to be fairly desperate for PIPs though to addle their formation for such a slight benefit.
Cheers,
Ivan.