Crossbreeding Indian Runners - genetics regarding upright posture

[davez]

I raise ducklings on 13% protein, week 3 I add some wheat , week 4 more wheat, etc. they all are from the same flock that was started from 1 drake and 2 hens. I have got a lot of big, chunky indian runners.

on the other hand ducklings that are hatched from small pullet eggs remained small (some of them didn't hatch or didn't survive).

Do they have acces to anything else? Like bugs from a pasture - are they in grass? Do they free range at all? Cause I would think 13% would be too low. But if they have any other source of nutrition, then they would pull from that.
Just curious about your experience.