I agree and I kind of think its helpful to have fewer nipples because multiple chickens can and will drink together at each HN - less water reaches the floor so the area under stays dry.I did an experiment this winter. I had one 5 gallon bucket with two horizontal nipples for 23 chickens. That's way more than the recommended 6-8 per HN. It worked just fine, though sometimes there was a line for the nipples. After nearly 3 months of this, I added 2 more hn's. They didn't seem to drink any additional water, but the lines to wait disappeared.
My thought is the 6-8 recommendation is very conservative. I've previously read similar recommendations for vertical nipples. I've also read recommendations of up to 15-20 chickens per vertical nipple.