Never had a BIR curry that improves on standing. A madras tasted the same when "fresh" as when heated up (or not) the next day.
Home cooked curries, on the other hand, definitely seem to benefit from at least an overnight wait. But so do traditional stews.
So what's the beef? It can only be that the pre-cooking used ubiquitously in BIRs effectively builds in the stewing stage.