Question on relationship of bulk ferment and final proof times especially in slow breads
Are there any "rules of thumb" for the ratio/relationship of bulk fermentation time to final proofing times?
For fast, straight doughs, I've generally found that the amount of time needed for the final proof is about half as long as for the initial bulk fermentation. Now that I'm experimenting with the "yeast and time equation" to convert recipes to slow ripened ones, I'm beginning to wonder about this relationship. If I convert a recipe to a 12 hour bulk fermentation, does that mean that I should plan on a 6 hour final proof?
The yeast and time equation that I am referencing is from this post: http://www.thefreshloaf.com/node/10876/long-slow-bulk-fermentationplease-critique-recipe  and the ensuing discussion on same at the A Year in Bread site: http://ayearinbread.earthandhearth.com/2009/02/math-is-not-hard-adjusting-yeast-for.html 
Somehow my mind wanted to think that the yeasties were happily and languidly breeding during bulk ferment and that the final proof should be similar to a straight dough. Not sure where I got that idea. Is this concept totally absurd?
I'd been happily baking whole grain hearth loaves and other crusty breads when my husband dropped the bomb that he really prefers a sandwhich style loaf for morning toast. So I tied out the ZolaBlue's Semolina sandwhich loaf http://www.thefreshloaf.com/node/4213/semolina-sandwich-loaf  . I didn't have any semonlina flour on hand, so I used spelt flour as the closet item to durum flour in my pantry. The loaf was delicious although I did not get quite the same ovenspring with the whole grain spelt flour. I tried agan with semolina flour but reduced the yeast to 1/8 tsp for a 12 hour bulk rise. (I prefer the taste and digestibility of a long ripened dough for our staple bread). It actually took 18 hours to double in the bulk stage, but only 3 hours to double in the proofing stage.
I am currently using the same basic proportions as the Semolina Sandhwich loaf but with a mix of White Whole Wheat (WWW) and whole grain spelt flours, using butter instead of the olive oil. The dough doubled nicely in the 12 hour bulk stage but looks like it will need 6 hours to double in the final proof. It's been in the oven with the oven light on for 5 hours now. I've been refreshing the pan of boiling water in the oven to keep it humid in there. The dough is just now cresting above the loaf pan. I'm guessing another hour before I can bake it. My main driver on the 12 hour bulk timing is to fit the baking in with my schedule. I mix up the dough at night, shape it after breakfast.
Any thoughts on the time ratio between bulk and final proof times? Anyone have similar or alternate experiences using the yeast and time conversion?