The efficacy of Quinclorac (drive) really depends on timing with the plants life cycle.
Research at Rutgers University here in NJ over the past 10 yrs since the inception of the material shows that from the 4 leaf to about the 5th tiller stage /early best efficacy is achieved /after 5 tillers the plant becomes too large and puts most of its energy toward seed production as it increases in size. As long as water is available for good uptake the 5 tiller control can be reached, if there is minimal water for uptake than usually the result is at 3 tillers.
When inflorescence (seed) finally pushes out the plant starts to reach the end of its life cycle and at that time Drive is effective again and will take it down all the way to the crown.
I have used this very research and it has been pinpoint time and again, in the mid stage when there are multiple tiller ( coffee can lid size ) plants Acclaim Extra ( phenoxaprop ) works the best for post control.
A strategy I use here in the north:
March 15 - April 20 / Barricade at .5 lb ai/a (Pre)
April 20 - May 31st / Dimension at .4 lb ai/a (Pre-post)
May 31st - June 20th / Drive at 1lb ai/a (post)
June 20 - August 15 / Acclaim at 28 oz /a (post)
August 15- mid sept / Drive at 1 lb/a (post)