I've heard things like that, and IMO I'm starting to think that the order of when you take them is crucial to whether to you have a bad experience or not (although 20 mgs would definitely be too much for me, let alone in combination).
5-Meo-DiPT has a much longer duration than MDMA, which is why I want to take it the way I am- I want the MDMA to cushion the ride back to baseline, but I want it to happen once I know I'm done with the foxy so that I can still enjoy the two of them seperately enough. I want the strongest part of the overlap to be in the middle of the night, so that the beginning and the end are still ruled by (predominantly) one chemical.
I hope that makes sense.