Warp point denial I
Pretty much. Only units "materializing in the same direction" can interpenetrate and destroy one another.
Now, I will admit that there is still a problem going back to those pesky closed warp points, because you can put material objects directly on top of a closed warp point and leave them there. So, in theory, your defense ought to work for closed warp points... which would also, just coincidentally, be the place where such a defense could be put into place without being sucked to the other side of the warp point. The truth of the matter is that the inability to do this on closed warp points was a designer's fiat when I first came up with minefields and other means of defense for warp points. It seemed to me that since the nature of open warp points as posited when I went to work on the game (and the original game I was further developing hadn't really said very much about them, one way or the other; they were just "there") made this defense unworkable for them, it would markedly unbalance the game if I allowed it to work for closed warp points. One of my developers argued that closed warp points already unbalanced the game in the favor of the aggressor, so this should be allowed as a workable defense, but he was voted down just about unanimously by the other twelve guys on my local playtest team. They felt that since the warp point could be located (and used) by anyone who saw someone else make transit through it, and since that was nowhere near as difficult as it should have been "in real life," allowing someone to basically park a garbage truck on it to completely deny its use to the other side would be much too great a defensive advantage to allow purely as an offset for how "hard" such warp points were to find in the first place. They offered me several possible rationales for refusing to allow it, none of which I found completely convincing on the basis of their internal logic.
Of course, one of my playtesters suggested letting the defender go ahead and use that sort of a defense but allowing the attacker to simply shovel garbage into his side of the warp point in even greater quantities. As the material came through from one side (which it would do effectively instantaneously), it would interact with the junk on the defener's side, and the resultant series of devastating explosions would basically "sweep" the zone of the closed warp point clear. I thought there was a certain elegance to this notion, but if I allowed it, all I would really do would be to create a situation in which both sides dragged their freighters/asteroids/whatever into place on both sides of the warp point and then spent a few dozen (or hundred) turns shoving stuff through before getting down to the regular business of an assault. The only real consequence would be that the time period in which the closed end of the warp point was busy imitating a star would allow the defenders to say "Gosh! Someone's coming through!" and rush to general quarters to receive the attack. That didn't strike me as being sufficient return (in gaming terms) for all of the elaborate rules which would be required (not to mention the additional time and "expense" the gamers would be put to) to justify incorporating the entire idea.