I've been on an on-off brioche quest for several years now. Recently I had a chance to bake with a professional baker, which really helped answer many questions for me (how much to proof, how long to bake, how much dough to put in the pan, how to knead, etc). I also finally solved the problem of the hourglass shape for pullman loaves that I have struggle with for years, and I've seen it reported on this forum by others as well. I've collected all of this into a very detailed brioche tutorial video. Thank you so much to everyone who helped me on this journey. I hope this helps someone with their brioche. https://youtu.be/O0a88_d8j-s
I'm passing it along to a brioche-curious friend. :-)
For Nanterre loaves I like to make the balls on the ends about 10% larger than the middle balls, so the loaf has a more squared-off profile.