bottom vs top (fill)
yes, i think Eureka's continual improvement of their uprights (ball bearing brushroll, rugulator/dial-a-nap) in the early 70s kinda forced Hoover to improve.
im reminded of the 70s Hoover ad with the hotel executive housekeeper. she makes it very clear that wood or aluminum are not acceptable agitator materials. guess Hoover was losing sales to Eureka?