I guess I'd describe it as "hot sensation". Yes, cleats are under the metatarsal. I can only move them back about half an inch, shoe design does not allow them to go any further. But I'll give it a try.
What do you mean by "tired" -- soreness, hot sensation, falling asleep? Are your cleats by any chance positioned in the "racer" position meaning by right around the metatarsal (a.k.a. ball) of your feet? If so, try bringing the cleats all the way down toward the center of your feet. This is considered by many as the most suitable for long-distance riding.