Control is the key-element of respondent large-scale systems to situations perceived as complex to satisfy the multiple operational conditions of use by any individual. Another perspective of this situation-system paradigm is derived in order to be applied to situations which may be perceived by their simplexity, meaning a portion of reality human-readable by detour. The indoor-air quality-control situation contains thus such phenomenological evidence of which its related framing by detour as a simplex-wholeness reveals the tangible togetherness on which all the contingent situations must be architecting as a system. We base the main modelling key-artefacts of this revisited situation-system paradigm from a body of knowledge in Systems Science, Systems Dynamics, Systems Engineering and Integrative Physiology. The coupling of the specification process with this affording reality brings out an interdisciplinary-wholeness resulting of the model-based orchestration of all the relevant encoding and decoding multidisciplinary knowledge. An early orchestration time points out the right oxygen molar fraction of indoor-air flowing in order to maintain a right hybrid-homeostasis for the occupant. The transition of the resulting mathematical model into a stock-flow diagram specifies then the balancing and reinforcement loops that a respondent-homeostat should satisfy to control the physico-physiological dynamics of this core situation-system from which a broader system may be defined. The increasing maturity of ambient technologies as well as modelling and simulation technologies make us intent for this type of application the perspective of coupling the in-situ source of the phenomena with an online or remote in-silico platform to better personalize indoor-air quality-control systems.