Excellent question! It is something like – your mind is superior to your senses.The senses can never know what the mind thinks – but the senses do have an impact on the mind. In the same way – the Bliss Sheath is the most subtle. It manifests completely only during deep sleep – during waking it manifests only a little. It is the where we experience a kind of negative Bliss – it is closest to the Atman.It also gives us waves of joy for no reason – that is the effect of past merits. Each sheath has its own function and it of course your breath and food can effect your mind and intellect- but as such, the other sheaths cannot have access to it – they remain in their own orbit.The food sheath remains only in the field of matter. The mental sheath is deeper than that – the food sheath has no access to its thoughts and feelings. In the same way it is explained that this is the deepest of all layers.