Maintaining ma-ai just requires practice at it. Don't wait for sensei to have a class on it, start now.
You can be proactive by 'controlling the first move' and encourage your uke to move where you want him/her to go. Smiles, fake a move, raise your arm, etc can be helpful to corral an uke.
Try to think of ways using your whole body/mind/spirit to have uke close the gap when you want it to happen. I like joking with my uke, then give him/her the ol' "come get some" in class.
Real life is a bit different.
Finally, I'd suggest the old adage: extend ki, or let your ki extend. I know many instructors whom you can _sense_ coming into a room because their ki flows so well. It's a GREAT way to control the flow of a confrontation.