Hi and welcome to the Chiari forum.
First it is very important to note that the length of your herniation is not the issue, the issue is , is the herniation causing an obstruction to CSF flow. Also, do you have copies of your MRI's and were they done at the same location on the same machine and did they take and review the same slices?
Unfortunately, Chiari is not something that is given much time to those medical professionals during med school, so not much is known by them....you need to locate a Dr that is doing their own research into it as well as related conditions.
I am not familiar with Drs in your country or how your coverage is for medical care....if you can travel to a Dr that specializes etc.....
May I ask, what symptoms you are dealing with at the moment?