The precipitating event through plot has to threaten the inner life of the main character. This is the kick-off in radio drama. The end or resolution in radio drama is more deeply rooted in the emotional equilibrium and insight of the main character. Changes are internal as well as external. Time transposition and translocation are faster and more rapid and more complicated.
Radio requires less rather than more characters.
Characterisation needs to be strong and fascinating. Maintain the focus of the main character and plot. Economy of words underlines subtextual surprise and engagement with the listener's imagination. Irony is pathos and bathos. It's conflict between the inner life and outer action.