In Simonini reaction how does the $2:1$ ratio of reagents enable formation of ester as major product?
If you have the extra equivalent of the carboxylate, then this carboxylate will never react with iodine to form the alkyl iodide. Instead, it will do the next best thing, which is $S_{\mathrm{N}}2$ reaction with the alkyl iodide that you did make.

Note that this probably only works if R is primary.