Mike
DFC 105 can be used as a pre-spray, an in tank cleaner and as a rinse agent. So it's 3 products in one for extraction cleaning.
After consultation with my distributor and Chemspec Europe, I work in a different way but still achieve excellent results.
Mix as a hot pre-spray @ 1:20 to 1:30 depending on soiling level. Agitate E/W & N/S with Envirodri, freshwater rinse, hot or cold
For the few licensed premises I do, rarely any blacktop & annually cleaned, 1:20, agitate with rotary, and DFC rinse @ 1:256.
You'll find a little more information on the Chemspec US website. They say that for in tank cleaning use at 1:128 (as per label) But they also say that if you are rinsing DFC 210 or DFC 105, then mix @ 1:256 in tank.
I have a large house in Worcester that I clean every year. Professional family with immaculate home. Never seen any "dirt" in the 24 years I've been going. So I mix as per label @ 1:128 in tank, spray carpet with wand then rinse/extract and groom. I only use a pre-spray on the entrance/hall.
Safe and happy cleaning

The Ken