Most Music Theory Books I have seen referring to the playing of a whole number of 'pulses' against a different whole number of 'counts' calls it "Artificial Grouping".(Hopefully that will assist with finding educational materials).
I started out with a basic triple on various divisions(3:2) - read as 3 to 2, then (3:1) ...then opposites...2:3 and 1:3 - simple seeming but it gave me the mental feel for one note over a triplet feel....something I had always been able to do but not with the sharp intention I wanted and later developed by being VERY mindful of 'feeling' both the 'pulses' and the 'counts' distinctly and unified...starting with either.
I then started getting a feel for 5's...aka quintuplets...over 2 through 10 pulses(and the inverse- really a mental training game) and then got really into it....playing {1 thru 10}:{1 thru 10} as an exercise...moving through different whole number combinations and ALWAYS working to develop a feeling for each as independent then as unified in my thinking.
I didn't do much else the summer of my junior year in High School...and kept up the development of feeling each whole number TO the next pulse on the list....then on to the next whole number combos.
I have never approached Fractional Artificial Grouping...and probably won't...i just 'transpose' the 'pulse' and 'count' to what is a whole number congruent ratio via Least Common Multiple or Greatest Common Divider .
In the end, your desire to learn Artificial Grouping will most likely be a unique exploration you design for yourself...or you will be looking at college training as few non-tenured teachers I have met can approach the subject with authority...or even cursory competence even though they have a strong grasp of triplets and, less frequently, quints.
A Couple of my favorite Drum parts that use what can be called Artificial Grouping(as we can conceptualize the same juxtaposed rhythmic values in infinite ways-literally) is Lethean by Katatonia from the 'album' Dead End Kings and a section in Anesthetize by Porcupine Tree from the 'album' Fear Of A Blank Planet
As a suggestion, try to avoid practicing just one rhythmic approach to the artificial grouping...work with different sub-divisions...then try to 'see' how 2:3 is much the same as 4:6 by switching from Crochet(quarter note) to Quaver(eighth note) Pulse...then work with changing how you mentally 'see' a grouping though you are playing the same thing.
Oh, and Gavin, if you are about, you should do an instructional video/material set on artificial grouping...it would fit in nicely with your other wonderful materials. I know you have approached it as 'Over-Riding' but I think there is a deeper understanding that you can lead folks to that explores the bi-directional nature (really, any number of directions) you can couple different whole number feels over different whole number pulses.