I see. I understand your position, but I read a bit different interpretation. In my opinion you must respect either restriction once you have touched the enemy TZ, not before. I have to admit the the verb "will enter" seems to apply to the movement before, but the full sentence says: "...will enter, or stars in, an enemy TZ must be completed once started". This means than either option included after must be completed. Certainly the 5th dot c) option is telling that the element must move directly towards the exerting TZ. I read that from that point on you respect it.
If I understand you correctly, you defend that figure 1b is not possible because element A did not move straight ahead its whole move before touching the enemy TZ. Is this correct?