Aloha richard1985,
An answer is to stay in your heart rather than your head. If that means that you just pick up with where you feel to, then do so. If that means to allow yourself to take another breath at the same location because Master Lin's Ohhm or muah is longer then your breath, then do so.
When he says "now we are coming to the ending," bring the energy ball from wherever it is at, around the small universe path to the lower dantain.
breathing energy into an area with an ohhm instead of a muah is like saying TOE-MAY-TOE or TOE-MAH-TOE. Communities or individuals may have a preference, but you still end up with a tomato, and the salsa along with your taste buds don't care in the end. It's all good!
That's not to say that various parts of the body are more receptive to, and respond more favorably to certain sounds or energies. I'm saying you don't have to concern yourself with it here, just trust in the universe and enjoy the meditation
Much Love,
Shawn