So one of the areas that I have investigated for the effect on facial development is the documentation in posturology. There are a lot of minor interferences that could potentially interfere with facial development. The question is always how does this play out structurally. All interferences play out in a disruption to the regulatory relationship between tongue, teeth/jaw and lips. The only way I can trace that posture could interfere with this relationship is by stressing the jaw joint, resulting in a lax position changing the tongue posture. I haven’t read anything about this that convinces me the supreme importance of posturology, nor can I dismiss it out of hand.
Posture is a really hard topic to find unbiased information about and I have not found a study that allows me to evaluate this idea properly. Part of the problem is that the factors that lead to the poor posture also happen to coexist with factors that directly impact facial development (like bottle-feeding). My inclination on this factor is to say that the minor stress from poor posture can be overcome with a high metabolic rate and a conscious awareness of jaw position.