Purcell's formula for the cavity enhancement of QED rates in terms of the density of states can be generalized to each position inside a cavity, and this local density of states can be explicitly evaluated for simple geometries such as a droplet. The density of states satisfies certain sum rules, which imply that when averaged over frequency and position, there can be no significant change of transition rates compared to the case of an extended medium.
H. M. Lai,
P. T. Leung,
S. Y. Liu,
"Cavity QED in microdroplets", Proc. SPIE 1726, 1992 Shanghai International Symposium on Quantum Optics, (28 October 1992); doi: 10.1117/12.140324; https://doi.org/10.1117/12.140324