Yes, dome fixtures do overheat, greatly shortening bulb life, especially with LEDs. I've always tried to let them hang down a bit leaving a small crack for ventilation, it seems to help. (I date my bulbs when I install them out of curiosity that started when I suspected (correctly) that CFL's only lasted about a tenth as long as claimed. Most of our LEDs, except those that went into enclosed fixtures before enclosed fixture bulbs became available, last at least as long as their rated lifetime.) LEDs that are not rated for enclosed fixtures will burn themselves up in a matter of months in a tight fixture.