Do you have the brightness most of the way up? If so it could be that the CRT is near the end of it's useful life, which at that point the electron gun looses it's ability to focus well. It's also dependent on HV, so it could be that your HV is still on the low side. Try dimming the room lights and see if bringing the brightness down helps sharpen the picture any.
Another thought is if the ion trap is on the neck reversed end for end it could be limiting your overall brightness.
Considering the amount of ambient lighting in your shop I'd suggest your CRT is doing it's level best at producing a decent picture. These early tubes were never intended to be watched in a well lit room. The screens simply can't produce a high enough level of contrast with the brightness turned up high. Just remember that the CRT face can only go as dark as the ambient light reflecting off it's face. In other words the CRT can't make it self go any darker, it can only lighten up. That's ultimately what limits your contrast. Hope that makes sense.
