I don't think you'll find any studies on the subject, but in my own personal findings, I think that any less than 67% of your total pwo mixture containing waxy maize, and you'll begin to see a noticable change in absorption.
One of the big benefits of WM is it's osmolality, which I believe is around 11 mmol/kg in a 5% solution. Compare that to blood at around 300mmol/kg.
What this means is it's kind of like a cannonball being shot at a fishing net, the fishing net just gets dragged along for the ride.
So, theoretically, any nutrient added to the WM will be "pulled" with the WM, hopefully increasing absoprtion rates.
The problem is, any amino based nutrient (protein, amino acids, creatine, etc.) has a MUCH lower molecular weight than WM. So, any added nutrients must, at least in theory, lower the total molecular weight of the "meal" that includes the WM.
Like I said above, I've found that any more than 33% of the total solution containing other ingredients, and you'll notice a change in absorption, based on blood sugar levels.
WM can be very beneficial in it's ability to pull water into the muscle.
Glycogen storage requires three things, sodium, water, and glucose (the WM is broken down to glucose in the small intestine).
WM seems to have the ability to increase the amount of water that is stored in the muscles.
For this reason, I feel that other cell volumizing ingredients are good to take with the WM. (IE: creatine, taurine, etc.)
An enzyme called "glycogen synthetase" is elevated for about 2 hours post workout (pulling from memory, may be longer). This increases the body's ability to store glycogen after a workout.
So, for these reasons, the WM is great for post workout usage.
My own personal WM usage is along the following lines currently:
110g WM
10g BCAA
10g L-leucine (shown to be the specific amino acid to stimulate protein synthesis)
10g creatine
15-20min after that I have the following:
50-100g carbs from oatmeal
30g whey isolate
10g BCAA's.
I've also experimented with WM usage at multiple points during the day. This would be done on days where carbohydrate intake would be elevated. The goal is maximal glycogen storage, and maximal "cell volumization" in the muscles.
I've been currently going up to 8 scoops total for the day.
I did this today, and I'm having trouble typing this due to the pump in my forearms.
NOTE:
This was written quickly, off the top of my head. None of the info was researched, or checked for accuracy.
Lately, I've been having people break down every word of my posts, and question me about any view that could be debated. So, before this happens, note my above comment.