My guess is that if you compare newborn babies by weight per body length you will find that MOST short babies will have fewer onces of weight per inch than longer babies do. Tall adults have more weight per inch of stature than do short adults. And 100 foot long crab boats weigh around 100 tons (one ton per foot of keel length), while 1000 foot long aircraft carriers tend to displace around 100 thousand tons (100 tons per foot of keel length).
So if you're gonna compare babies by weight/size wouldnt it make more sense to plot their body weight,not against body length, but against the CUBE of their body length?.Your weight is proportional to your volume, not to your linear height.
Lets say its fish. You wanna know if fish B is scrawnier than fish A. Fish A is X inches long and weighs Y number of pounds. Fish B is 2X inches long. If it had the overall same proportions as fish A it would weigh, not 2Y pounds, but 8Y pounds (because its width, and height from keel to upper deck would also be twice that of fish A, giving fish B eight times the volume of fish A). So if fish B is only 7 times as heavy as fish A then you know its less robust in body proportions (scrawnier).