I have been using 20 HFT’s in my system since around June 2021. 20 of these buggers. That makes level 4. I am enthralled! My sound stage has expanded and moved forward and in some instances is like I have headphones on. Sometimes I need to make sure my surround is not on. My bass is better. More separation of vocal And instruments. This all in 2 channel and no subs. EVERYTHING I throw at my system drops my jaw, regardless of source.
20 is about where I'm at. Two speaker kits plus however many room. This is after years of experimenting with various panels and tube traps. HFT are far more effective than those old school treatments. Plan on adding some diffusers some day but for now I am like you, swimming in it.
The recommended placement program works great, but within those recommendations they are surprisingly responsive to positioning. Mine were put up in pairs and sometimes one at a time, with each one being moved slightly an inch or three and always noticed a change sometimes surprisingly big. One on the back of my old Talon Khorus speakers went from great to awful by moving a mere 2"!
The champeen of HFT is David Pritchard, who used to be a quite active poster. He had dozens in his listening room, all over his mom's place, and even in his car!