@wilddeath I have a problem with that explanation as well.
During the tournament before he fought Rennes, remember Rennes visits Xiang Ye to convince Xiang Ye to give up on Yi bei. This was chapter 111 and 112. At that point in time Xiang Ye was still visibly affected by Rennes Boundary Force. To the point where he couldn't move. Yet a few chapters (in the 140s) later when they are actually fighting each other he is completely immune to an even greater amount of boundary force put out by Rennes.
Even if you assume the useless Lumbar mech suit that he was wearing could block some of the force, his helmet was destroyed long before the end of the fight so certainly he should have been affected by the force at that point time. Remember this was a generated force strong enough to withstand an explosion that had to be contained by a Dyson Sphere, basically the power of a star going super nova. Yet Xiang Ye was able to ignore that amount of boundary force with no problems.
So the only event that occurred between the meeting in chapter 111 and the fight in early 140s was Yi bei becoming Isabella temporarily before she is rendered unconscious by the Principal. The problem with that is she is immediately transformed back to her human form after that point so it wouldn't make sense for the ring to suddenly start working just because she changed to Demon Queen Isabella once. Remember when he was initially given the ring she was still Demon Queen Isabella, so if her temporary transformation was the catalyst then he should have had the ability to resist Boundary Force the entire time.
The point where it would make the most sense for him to gain Boundary Force immunity would be when the Principal let him know that the rings contained enough Boundary Force to allow him to transport back to his original world. The problem with that is he got that information in chapter 109 which was before he was affected by Rennes boundary force in chapter 111. So unless the order of events was screwed up, or he wasn't carrying the ring at that time for some unknown reason, it doesn't make sense that he was vulnerable to Boundary force, at one moment and then immune to it the next moment.
Also there are other points during the entire race arc before the fighting tournament where he would randomly be immune to boundary force which, again makes no sense.