arXiv:2610.31204v1 Announce Type: new Abstract: Grid-interactive buildings can adjust demand, but building-feasible power budgets may differ from accepted feeder-head offers. This study addresses a practical question: to what extent can the adjustable electricity consumption of buildings be translated into deliverable flexibility services while satisfying feeder-head operating requirements? To enable a fair comparison, we adopt the same baseline operating schedule, equipment conditions, and post-service recovery requirements for indoor temperature and battery state of charge (SOC). Flexibility is then evaluated under two settings: one considering only building-level constraints, and the other additionally accounting for feeder-head constraints. We first use a simplified network model with explicit security margins to determine a preliminary amount of flexibility that can be committed. The resulting schedule is then validated using a more detailed network simulation via Modelica. If network losses cause the actual response to deviate from the committed response, the electricity consumption of individual buildings is rescheduled. If the required response still cannot be achieved, the committed flexibility level is reduced. The experiments cover multiple service activation times, regulation directions, and service durations. For comparative purposes, we retain the initial optimization result as the reference estimate of the maximum potentially available flexibility, rather than interpreting the failure of a particular subsequent realization attempt as evidence that a larger flexibility level is inherently infeasible. The results demonstrated that 24.51\% of nonzero flexibility contracts were rejected due to feeder-head constraints, 67.04\% of contracts were accepted with some rescheduling and building redispatch, and only 8.09\% of contracts were accepted without any changes.