Number of convection zones

Stellar structure modelling: No convection (neither in A- nor in F-stars)
convection zones are shallow and do not affect the radius
Stellar atmosphere modelling: No convection
stratification essentially radiative
Element diffusion modelling: One convection zone
both convectively unstable zones are coupled (by overshoot?)
(Local) mixing-length theory: Two convection zones
two convectively unstable zones