I've read what Fon Tok Nak said, and realise he's right and I'm wrong.
In particular, moving blocking elements out of the way only happens after contact has happened, in order to allow contacting elements to conform.
Given the situation outlined in the OP, there are two possible solutions for Alexander to get to Darius:
1. This bound, move Alexander backwards in accordance with the TZ rules until he's well out of Darius's TZ; next bound, move Alexander into contact with either the Hd element or the Ps element; after destroying that element, move into contact with Darius (if he's still around).
2. This bound, move a group of elements into contact with either the Hd element or the Ps element in such a way that when it conforms to the group it widens the gap enough that Alexander can move through the gap this bound to contact Darius.
As Fon Tok Nak says, there has to be a space rule, and the rule is a base width.
It may be worth taking a step back and considering the broader tactical situation. Alexander's facing three elements, and he wants to get to the one that's behind the other two. If he wants to do it all himself, then it's going to take time by going through the one of the elements in front and then getting to Darius (if he's still hanging around). Otherwise, if he wants to get to Darius this bound, he's going to need some other friendly troops to help him.
So regarding your questions 2 and 3, I don't think an extra rule is required beyond what's already there. The issue is not so much that the arrangement of Persian elements has set up some sort of impenetrable TZ that prevent Alexander from attacking at all. Instead, the arrangement of Persian elements has set up a situation that requires Alexander to back off this bound and come in next bound at a different angle (or call in some friends to help open the path this bound). Given the tactical situation Alexander is in (outnumbered 3 to 1) I think that's a reasonable pair of alternative resolutions.