I'm having an issue creating a VAV and Air Terminal family using instance parameters. Essentially, I want the size of a VAV and the size of an Air terminal to be determined by the Air Flow (CFM) ex. If Flow < 320 then the neck diameter of the air terminal will be 8". I was able to do this successfully but I'm having an issue when I connect to a system. Since the air flow is an instance parameter (can't use type parameter since the air flow is different for each air terminal) then the neck diameter has to be an instance parameter as well. When I type 320 CFM as the air flow value, the air terminal automatically makes the neck diameter 8", perfect so far, but if I accidentally take a 10" round duct and connect it to my air terminal neck, the neck size changes from 8" to 10". I'm having the same issue with the inlet and outlet dimensions of my VAV box. Everything sizes correctly based off the air flow, but if I connect a different sized duct to the equipment then my inlet/outlet/neck diameter change to whatever size duct is connecting into it. Is there a way for my families to still automatically change dimensions based off the air flow while also preventing any change to the neck diameter/outlet/inlet sizes due to a different sized duct connection to the equipment? I was able to successfully prevent the neck diameter/outlet/inlet size from changing due to a different sized duct connecting to the element, but I only achieved this by changing the parameters from "instance" to "type" which forced all of my air terminals to be 320 CFM, so this approach didn't work either. I'd appreciate any advice on this matter.