Bingo!!
It is all about cartridge pressure. When pressure is applied to a fluid that pressure is equal and undiminished in all directions. Naturally that pressure will seek out the path of least resistance in order to escape the cartridge. The low pressure (escape) areas inside the YZ cartridge exsist in the following order. Compression adj. bleed, CV, Base valve. The midvalve creates resistance as it travels through its stroke but the pressure within the cartridge is being produced by the damper rod entering the system. If the midvalve is set up to create excess resistance (greater than the base valve) it will also be responsible for cavitation within the cartridge. So, after the flow capacity for the comp. adj. has been reached the next path for the oil to escape is through the CV. Now, since Yamaha have been using the CV they have nearly tripled the stiffness of the base valve from previous models which all the while promotes oil emission through the CV. The problem is the flow through this valve is too great. The port growth area is huge in comparison to the base valve and the shimstack is fairly light with quite an area available for deflection. Naturally on big hits the oil exhausts from the top of the cartridge and the fork can fall through its stroke and bottom out too easily. So, knowing this you can see why I don't care what bottom out system you use. The fault lies in the fact that your forks are getting to the bottom out system too easily in the first place. Ask anyone that rides the blue beasties and they will tell you that they feel harsh, yet bottom easily. In order for the CV to work effectively I would like to see it have a reduced flow capacity. This would control bottoming more effectively and allow you to run a lighter base valve.
Regards
Terry Hay