Don't know about the WW2 chest mounted 'chutes, but the modern chest mounted reserve suspends you from its' mounting point on the harness at chest level.
Remember being a bit concerned that this would just deploy up & into whatever bag of laundry my main had become, in the event of a drama. Despite the PJI's re-assurances, I was determined to cut away the main 'chute before deploying the reserve......glad I didn't have to.........
HB