Measuring Heterogeneous Adaptation: From Nominal Configuration to Intervention Dependence

Modern frozen-backbone adaptation systems combine heterogeneous controls, including available transformation banks, conditional allocation, and learned prompt-derived states. For such systems, nominal capacity scalars do not identify mechanism usage, intervention dependence, or downstream utility. We study how nominal configuration, structural availability, conditional allocation, realized actuation, same-checkpoint dependence, and downstream utility should be measured separately. We instantiate the study in VEFT+, which exposes these controls to observation and intervention. By varying residual-transformation availability ($K$), the number of subnetworks, and soft-prompt conditioning capacity ($\text{sp\_len}$), the number of prompt states, we examine whether configurations with equal nominal products yield equivalent mechanism use or utility. Within the evaluated configurations, increasing either $K$ or $\text{sp\_len}$ does not produce a metric-independent ordering, learned nonuniformity does not consistently outperform uniform composition, and evaluation-time prompt removal is not equivalent to training without the prompt branch. Ultimately, nominal allocation, realized composition, intervention dependence, and downstream utility operate as distinct properties in dual-axis adaptation.