I should have included a reference to the original plugin announcement, which is where I learned of the relative nature. I recommend reading the first 3 to 5 posts in that thread. CuteFox Modules - Intervallic Pair Quantizer | Release
Depending on the gap between the previous quantized note and the current input, it may not be a single interval that is being used. It will be a series of alternating intervals. I suppose the module could indicate whether the last interval used in the series is #1 or #2. Maybe that is what you are looking for? (remember, I am not the developer)
I believe if the current input is higher than the previous quantized value, then the first interval in the series is always #1. And if the current input is lower than the previous quantized value, then the first interval in the series is #2. That makes the most sense to me, though I haven’t tested to confirm. But the last interval in the series is dependent on the size of the gap.