Train. A lot. You've got good teachers, so trust in what they show you, try some things out after class. See what happens, and figure out what works.
Beyond that, you are correct...aikido as you see it in the dojo is probably not how it will work out if someone decides to take your head off. I think you've got a good base for dealing with this in getting offline, setting and controlling the ma ai, moving proactively. The devil will be in the details, especially when the situation is bound to be chaotic. Some things to think about...
1) My teacher always says NEVER LET someone grab you if you are defending yourself.
2) Think about cutting down your attacker, cutting their attacks, cutting their neck, keeping them off balance by entering and cutting.
3) If you make your attacker keep turning around to attack you, shomen ate / shomen tsuki / face thrust irminage is an excellent tool. Thus evasion while entering to get behind them, then entering as they turn to face you can work very well. Control the head as you enter...their body usually follows.
4) Buy a pair of track shoes. Wear them often.