Allison, just to clarify a couple of points you asked about: the fact that your tumor extends into the cerebellar pontine angle (CPA) possibly makes a retrosigmoid approach more likely, but otherwise is most likely not significant. Anatomically, the CPA is just the space between your brainstem and the little holes in your skull that the cranial nerves travel through on their way to your facial muscles, ears, etc. So it sounds likely that your tumor started in your intra auricular canal (IAC) and has ballooned out via the path of least resistance into the CPA, where there is some open space for it to grow. Tumors in the CPA can get very big -- you heard about Jim's, and mine was in the CPA and over 4 cm at its biggest point. So comparatively yours is still on the small side and therefore possibly a candidate for radiation.
Any balance problems you are experiencing come from the tumor interfering with nerve signals. It's very easy for that to happen in the small space of the IAC. Getting into the CPA probably wouldn't increase the balance problems because things are packed less tightly together than they are in the IAC, but it does make it possible for the tumor to interfere with other cranial nerves that pass through the CPA. One reason that surgeons like the retrosigmoid approach is that it affords a good view of all those nerves and, therefore, how the tumor may be stuck to or otherwise interfering with those nerves.
You mentioned eye twitches... I would guess that this comes from interference with the facial nerve (which controls movement of most facial muscles), which travels through the IAC, or possibly the trigeminal nerve, which controls, for the most part, facial sensation. The trigeminal nerve does not go through the IAC, but it does go through the CPA.
I don't know if any of this is helpful or not. Hopefully it is... I know that for me knowledge was power when it came to my tumor.
Good luck with your appointment and decision making.