Hi as I have mentioned mine was 4mm's on one side and barley 6mm's on the other....if you have a true Chiari specialist and are having symptoms they will look into other possible reasons for those symptoms....I also have a partially retroflexed odontoid which makes it even tighter in that small space for CSF to flow....
I went to several Drs prior to finding my surgeon and was told I didn't have Chiari that my issue was bulging disks, and not to let anyone touch the Chiari....?? If I didn't have how could they touch it?....The next one was in Philly and was a supposed "expert" or specialist....he said I did in fact have Chiari , but it was "above" him...he couldn't help me and could not suggest where I go next.....
Most of us will have a similar story of seeing Drs over different periods of time and being denied a DX or a belief the DX is causing the symptoms/issues we present.....