A question about retarding 30% starter sourdough

Hi Bakers,

My question is actually two questions.

I am baking a miche of 40% bread flour, 40% whole wheat and 20% rye, 70% overall hydration, 2% salt, 30% starter and 18% grains.

Starter is 100% hydration (same flours %).

I've baked hundreds loaves with this recipe and now the questions are:

1. Most recipes in Hamelman calls for about 15% starter. Only rye recipe contains up to 30%. what does it mean to have 30% starter in the recipe. What would happen if I change to 20%? (tried, did not see a big difference).

2. I am retarding the loaves occasionally to be able to use my schedule better. Hamelman is talking about retarding in 5-10C while a regular refrigirator is 3-5C. Now, my question is: if the recipe calls for 3 hours of final proofing, what whould be the corresponding time in a refrigirator? Is 6 hours enough? Hamelman is talking about up to 12 hour but what is the minimum? Can I use 1 hour of regular proofing (after 2.5 hours of bulk fermentation) then x hours in the regrigirator? What's the rate? Is there some kind of a rule?

Thanks a lot,

David