“Level”, “Groupings”, and “Ratios” all introduce polyrhythms in the comping, and are categorized differently for ease of use.
Going through the Levels, you have control of how complex the rhythmic comping is going to be, but you do not get to choose the actual polyrhythms used in it. On level 1, you get no Polyrhythms, on Level 2 simpler and more common polyrhythmic phrases are being introduced, such as dotted and 3:4, and as you move up the levels, you get a bigger variety of more complex phrases like triplets in groups of 17.
Using Groupings and ratios, you get to choose the specific polyrhythm that is going to be used during playback. The Grouping or Ratio that you picked will be the only thing used when the Genius Jamtracks trio decides to throw in a polyrhythmic phrase. Groupings refer to actual note values, eighth notes, quarter note triplets, etc., and how many of them it takes for the rhythmic cycle to complete.
Ratios refer to the relationship between the rhythm of the song and the rhythm that is being superimposed on that. For example, let’s say you have a 4/4 measure. One rhythmic layer uses the 4-beats reference for that measure, and the second divides the same 4/4 measure into 3 beats. This is referred to as a 3 against 4 or 3:4 polyrhythm.