98mm boots tend to be simply wide versions of a company's world cup fit, so the free space around the navicular and/or medial ankle bones is very minimal. Because the shell therefore sits closer to the foot, the first step is 100% making sure your footbed is dialed and if you don't have one, you really need to get one. 2-4mm of ankle movement can ruin your day in a 98mm boot, so make sure you properly stabilize your foot/ankle with a footbed. If your footbed is in place, then you will need to (most likely) have the shell stretched/ground in that area to make enough free space around your ankle.
To make sure what I am saying is accurate, you can do a simple shell fit at home: remove the liner from the shell, place your footbed in the shell, step in while wearing a thin ski sock, and notice where & how your medial ankle comes in contact with the shell. If there is no gap between your inner ankle and the shell, you will need to have the shell modified in this area, and that means making a visit to your boot-fitter once you are able to do so. If there is a 5mm gap, then you are probably ok and it is just a matter of the liner breaking in.