Focus of the eyes during deep meditation

I know that principle #1 is to focus on the mantra. But what should one do about the focus of the eyes? When the gaze moves downward, it feels sleepy. It they are focused with an upward gaze it seems become strained. In a sense I notice if i just completely relax them, it’s like the eye muscles turn off completely, but it is possible to become tired. Also you could just look straight ahead.
What is the best technique for increasing mental focus without straining the eyes?

Gradually work your gaze up. The body takes a very small time to condition itself to a certain position. Gently insist that the eyes look up more and more over time and there shouldn’t be much resistance.
Also, the energy flows in the body might not compliment this mudra just yet. If you feel compelled to keep your eyes forward, by intuition or discomfort, keep them forward.

Hello Iced Earth,
During AYP deep meditation we don’t worry at all where the eyes go, so if there is tiredness and we lose the mantra temporarily that’s fine, we just pick up the mantra again as soon as we become aware that we are not doing the mantra. The point is not to keep mental focus during the meditation. Awareness and focus will come by itself through inner silence, not by trying to accomplish it by force (in this case, however there are other methods of course to develop mental focus as well).