How much do you weigh? Above a certain positive air spring pressure, it is very hard to dial in enough negative pressure AND keep the fork from rebounding harshly at topout. I use the middle ECC setting since the 4th position starts to exhibit the lockdown "grab", and the 2nd position is totally uncontrolled rebound. I'm on 10wt oil now trying to slow it down. I also think the ECC could be improved with an adjustable rebound screw so you can change the settings at each ECC click. And for the A to C height of the fork, you could be getting close to an inch more travel with the new 5.5-6" travel forks coming out. Oil seeps into the negative chamber over time and reduces travel. I like my Z1 SL, but it does have its deficiencies. If you spend a lot of time tuning it, you can make it ride nicely.