This is currently most common, though I hope this will change. I had even bigger specimens of elks. And in case of reindeer it is quite common to get a calf weighing more than its mother. Size of skin is not related to the body size at all. Skin size is constant for adults, and for calves it has only a handful of values apparently, for example for elk it is usually 2.47 lbs, and value is 23.33 units (which is the most common value of skin for reindeer calf too, though they have smaller skins).
I have met only one sizeable reindeer calf, which has skin weighing 7 lbs and costing 140 units (i.e. 70% of adult values), it also was weighing 70% of species average. I suppose this is how it should work - but it was unique occurrence, in most cases it is a small skin costing 23.33, and a big, fat calf. Still, meat is expensive and fast to process, so they are not total waste of time.
EDIT: I looked at two cases of elks and bears, and it's even funnier with them than with reindeer. In both cases the cub was quite big, exactly 70% of species average for its gender, and here's the thing - it was a male, which is bigger in elks and bears than females. In case of bears this means that EVERY male cub will be bigger than its mother, unless she's above average, or it's very young (I haven't met a very young bear cub, only these seventy-percenters). Average male elk is 300 kg, female is 250 kg, average male bear is 240 kg, female is 160 kg (this changed quite recently, previously all bears were 180 kg on average). When converting to lb weight is multiplied by two and rounded up, resolution of weight differences is 1% of average size.
My two specific cases:
Elk mother 390 lbs (skin as usual 21.21 lbs, males have it at 23.33 lbs), elk calf 420 lbs (skin 2.72 lbs, i.e. 1/8.57 of adult male size).
Bear mother 263 lbs (skin as usual 23.33 lbs, males have the same size), bear cub 336 lbs (skin 2.72 lbs, i.e. 1/8.57 of adult size, like most skins from calves and cubs). As a side note, bear skulls weight 1% of their body size, meaning that the skull from the cub was bigger than from his mother too.