CW, this is the problem. You are confounding "being in deco" for your body with "being in deco" for your computer. If you set the Perdix to 75/75, of course it will show deco if you get to 76% of the m-value. But by your definition, you are not REALLY in deco until you hit 100% of the m-value. You really can't have it both ways......your Teric is showing 99% of the m-value, your Perdix is showing 75% of the m-value.To me, I’m not in deco until I have exceeded m-value.
It is like the old days when people learned about deco diving by wearing two computers, one set to air, one to Nitrox, which was the gas they were actually using. They watched the air computer for their dive, and it went iknt "deco," and they learned to follow the instructions on that computer to learn what it showed and how to hold stops, etc. But since they were on Nitrox, they were never really in deco.....it is just that the air computer thought they were.
Your Perdix at 75/75 thinks you are in deco. Why is this a problem? You TOLD it to say that!