The functional residual capacity is made up of expiratory reserve volume (ERV) plus the residual volume (RV) - i.e. the volume of air remaining in the lungs after passive expiration.
Compliance of the lungs is said to affect FRC. For example, if compliance of the lung increases (e.g. in emphysema), there is less elastic recoil and less air is passively expired, resulting in increased FRC. Could one explain this as increased compliance (where compliance = ∆V/∆P) meaning that the same intrapleural pressure at end of passive expiration results in a greater lung volume (FRC) at that time? This seems to explain instantaneous volumes rather than the actual expiration of less air.
How does this translate to compliance of the chest wall? As recoil of the chest wall tends to be outwards, would reduced compliance mean that there is greater tendency to recoil outwards, making intrapleural pressure more negative and reducing expiration of air, leaving greater FRC?