Any basement even visably dry may be to wet to close up resulting in
mold, get a moisture meter and test your walls after big rains. If dry
you don`t want an air gap, I used 2" R 7.2" foamboard for R 14.4. on
basement walls, much thinner than fiberglass, On damp areas it is all
designed for easy removal and future repairs. Another consideration for
foam is pipes brake , basements flood.