Happens to me sometimes because i can't easily attach TrackIR to my monitor properly and that limits its field of view.
Make sure you don't stare at the monitor from 10 cm like I sometimes do :lol: . If you do: get back as far as you can and press F12(by default that's center key) and try zooming in from there.
Also you can try pointing TrackIR down a bit so there is more field of view on zooming downstairs part (I don't think you gonna need a lot of extra space upstairs coz you don't need to stand up in the plane :D)
I think you can get used to it after some time. Once i was flying on KA-50 for some hours for practicing using TrackIR. After some point i forgot i was practicing and it became kinda natural. Next day i didn't enable TrackIR and it felt so unusual to use mouse again. But i was too lasy to enable TrackIR so I got used to mouse again :D