Yes, that is AiH's 9" slotted false bottom. I brew mostly 3.75 gallon batches. However, I do brew the occasional 6-gallon batch.
I used to use Phil's Phalse bottoms in 10 and 7-gallon Gott coolers, which were basically plastic versions of the dome-shaped perforated steel false bottom that is sold for 10-gallon coolers today. The best extraction rate that I could eek out with a perforated false bottom and imported malt was a mixed-grist rate of 31 points per pound per gallon (PPG), and that was a rare event. My consistent mixed-grist extraction rate was 28 PPG. With the slotted design, my consistent extraction rate with imported malt is 32 PPG, which is kind of a sweet spot for me. I actually have to be careful now to prevent going too high. I have hit 35 PPG with a mostly continental pils malt grist. I personally believe that a beer starts to suffer at that extraction rate, at least in my brew house.
Besides having an open space of 16%, I believe that lot of the improvement in extraction rate is due to the fact that the slots are difficult to plug. I used to have spray water through my perforated false bottom after dumping the grist because so many of the holes would be plugged. Plugged holes lead to uneven draining. Uneven draining is not a problem if a brewer batch sparges, but it is an extraction rate killer with continuous sparging.