Minderwiz
I was using a more modern convention that seems common here in the U.S. The slower moving planet is seen as the base or root or reference planet. The faster moving planet is the one making the aspect. So, in my examples, Jupiter is the slower planet of the two, and Mars would be the one making an opening square (90 degrees ahead in zodiac position), the opposition, or the closing square (270 degrees ahead in the zodiac). This seems based on phase relationships, and may also be the convention advocated by others. However, many years ago I disposed of some 350 astrology books (I didn't have the room for them), and now I have no references for these details. Dave
The phase relationship is still there in the Hellenistic/Early Medieval. In the example I gave, when Mars in the dominant position it is a closing square in your terminology and making its way to the conjunction and when Jupiter is dominant it is an opening square in your terminology, Mars having separated from the conjunction. In the case of the Dominant square, Mars is looking forward to Jupiter, as both planets usual motion is through the signs. Jupiter has to turn round and look backwards at Mars coming up behind. As any fighter pilot knows, Mars on the tail of Jupiter is in the stronger position.
Remember that sometime around the millennium, the direction of dominance seems to have reversed. There doesn't seem to have been any rationale for this, so it was probably a copying or translation error.
It is the latter (probably wrong but certainly without a rationale) interpretation which was !ost likely transmitted through Lilly and other late tradition Astrologers (who had no conception of fighter pilots) to the modern day.