The Montauk daisy (Nipponanthemum nipponicum) is prone to flopping when flowering, by cutting back in May and then again in July
The shortened stems display the fall flowers at their best
I also prune (once) our Fall flowering Asters for the same reason. This is the new growth from an early June cut back.
This year I am cutting back some of our Sunflowers (last week)
or they can rapidly grow to four feet and swamp smaller plants
At this time of year, (before flowering) I am never sure if we have Helianthus, or Heliopsis
I should hedge my bet and claim them to be Heliopsis helianthoides