in my experience with blackstar amps, the ISF goes from wider (british) to more focused (USA). but it still sounds more like a Marshall tone to me even full USA, and definitely not like a Rectifier. i was lucky enough to own a dual rec, a stiletto and a roadster over the years. my friends always used Blackstars and i sold tons of them when i managed a music store here. i would never try to get a Recto tone out of the Blackstar amps.
instead i'd try the BRIT JVM, either Orange or Red channel. it might be exactly what you're looking for.