Joglazier, are you using a cheater in your hood? Do you have bifocals in your prescription glasses? If you are old enough to have been welding 27 years I would think that you would need some kind of magnification for close up work, reading, welding, etc. especially in poor light. Typically overhead will be in a shadow , the light being above.
The problem is that as we age our eyes loose some of there elasticity and can't focus as close as they use to. Without getting over MY head, it is like a camera. When there is a lot of light our pupils are small, like a camera stopped down. We have a large depth of focus. In other words, the distance that we can see in focus, near to far, is greater in good light. When the light is poor our (over 40 years) eyes began to loose the ability to focus in close. To carry the camera analogy a little futher, in poor light the lense is wide open, to get as much good light as possible, but the debth of focus is small.
So what may be happening is that the bad light on the bottom of the weldment is not allowing your mature eyes to focus clearly. Having the right cheater (magnifier lens) should bring overhead and any other welds into better focus. I rememer on old welder that refused to wear glasses or a cheater. His welds would run off the center of the joint. He was a good welder but was sure having trouble making welds. It was sad to see him struggle with his welds.
If cheaters do help, you might consider having several different strengths. They start at 1.0 and usually go to 3.0. Close up welds like low amp TIG, I might put a stronger cheater in. High amp MIG where my head is futher away from the weld, I might put in a cheater of lesser strength. To find the correct one, look at small print at the distance you will be welding at. Try that in poor light.
When I first used a cheater a 1.0 or 1.25 worked great for everything. But as the years have added up and I've gone to stronger and stronger cheaters, the correct one is more critical. As the magnification becomes greater, the debth of focus becomes smaller. That is why when you get into the stronger cheaters it is critical to have the right one for the distance your eyes are away from the weld.
Hope that helps. Good luck.