Peter - Thanks for the reply. My original idea was to use less starter because I did not want the dough to expand too much. It is obvious from all of the other DD recipes I have seen that significant expansion/fermentation would detract from the desired texture.
When making panettone using natural leavening, the high fat and sugar environment requires you to get the starter to a hyper active state before being used. You feed it 3-4 times a day for two days straight, to the point where the starter is tripling within a few hours. I obviously don't want to do that just to make DD, so some sort of balance needs to be found. The difference in taste was noticeable enough that 20% starter seems to be a good reference point for 8 hours at 68 degrees. I might try upping the oil and seeing how the starter responds, and then make a determination afterwards to see if the increased oil is what I want in the final product.
But that may be a while from now, because I can only tolerate these giant casseroles once a month or so!