Can you give more detailed examples of this? There's a possibility that your equivalency is off, because quite frankly I don't know what you mean. There are also cases I believe where someones tolerance might be too high to even get off on a weaker opiate. For example, I have only been able to get high off of hydrocodone two times in my life, though on several of occasions I have taken massive dosages of it. However, I have always been on Heroin, Methadone or Bupe, so my tolerance was pretty high. I remember even being dope sick once and I had found a whole bottle of 7.5 Vic's, I don't remember exactly how many I took, but it was a lot, and I don't even recall them getting me well. Similarly, there are certain opiates that have a ceiling dose, like codeine, so if your opiate tolerance is far beyond the equivalent to that ceiling dose of codeine (400mg or so), then you shouldn't even bother. I also feel like for me, certain opiates/opioids will just never do anything for me, like tramadol.