Oh, that kind of low spots

I normally make the belly follow the growth on the back. After all, it doesn't take many millimetres for a section to become too stiff and then putting the stress on the thinner places. I would make a section with a knot or other weakness in it thicker, but if it is only the wood fibers that fluctuates I don't see why one should stiffen such a section of the bow? It would definitely make it quicker to make, but I don't think it is the best way to distribute the stress as evenly as possible?
Alanesq has a nice web page dedicated to the side nocks of the MR.