Since the theory is that the less flamable stuff should be toward the middle, the thing to do is to put a match to the leaves you intend to use and find out which are the more flamable and which are the less. Like most/all things in rolling, better to just check it out than go with theories. Some ligero burns great and some seco doesn't burn worth a sh**.
As for the original question, given the leaves from one particular, actual plant, I would guess that the seco will not be thicker than the viso. Beyond the leaves you have from one exact plant, all bets are off. Of course that's not going to be your typical situation unless you grew that plant, plucked it, cured it, fermented it, bagged it.
Oh, and as for the theory of where the flamable stuff should go? I often stuff the seco tear-offs into the middle and the thing still burns evenly and well. So... it's all down to trying and finding out.