As described in my other answer, the OSHA guidelines cover pretty much any size monitor. However, people may have an extremely large monitor they want to use from a closer-than-recommended distance, or have unusual workspace constraints, or want to experiment with placement. Here is a useful way to approach monitor positioning if you don't want to follow the OSHA guidelines.
Start with you
Monitor placement begins with the user, not the monitor or its size. The requirements are driven by characteristics of the "human machine". Aligning the top of the screen with where the operator looks straight ahead is based on human physiology, not monitor size.
There are movements that are easy for your body to do and ones that are stressful. Tilting your head up is more stressful than tilting it down. Rolling your eyes up is more stressful than rolling them down. You can look down about 35 degrees without moving your head, and about 60 degrees comfortably if you move your head.
Ignore the monitor for a moment. From a "neutral" position, using good posture and looking straight ahead, it is easy to look from a range of straight ahead to about 35 degrees down. Call that your neutral field of vision. Outside of this range, it is easier to look down than up.
So you have four "bands" to work with:
- straight ahead to 35 degrees down: your most used content
- 35 to 60 degrees down: as much of the rest as you can
- above straight ahead: last resort area
- below 60 degrees down: another last resort area
Anything outside of straight ahead to 60 degrees down will need to consider what you find the most comfortable and any limitations of your workspace.
Add the monitor
Now superimpose the monitor. If the screen is larger than the neutral field of vision, your body will need to do work to look at the rest of the screen. There will not be a perfect setup; you will need to make compromises. The tradeoff is a combination of:
- how far from ideal you need to position things
- how often you need look at the things that are not in ideal positions
- how stressful it is to look at those positions.
Any "optimum" solution, regardless of monitor size, will involve having very little screen above straight ahead, or below 60 degrees down, although needing to occasionally look in one of those areas may be part of the tradeoff.
The premise here is that you want to use the screen closer than recommended. If there is any way to work within the OSHA guidelines, that will give you the best result. So before settling for a compromise, challenge your assumptions that you need something different. Look for a way to adjust your constraints. Just sayin'.
If you use glasses and your vision is what's driving a need to use the monitor so close, get a pair of computer glasses, which will give you a full field of vision corrected for the monitor distance you use. This will allow you to move a large monitor a little farther away and compensate for the distance with the prescription. That puts more of the screen within your neutral field of vision.
How you use the monitor can be a major factor in the equation. If portions of the screen must be in places that are stressful to view, it will be tiring and possibly uncomfortable to use for long periods. You can improve the situation by controlling where you place things on the screen. Use the areas outside your neutral field of vision for what you use the least often.
For example, say your situation requires that a small portion of your screen must be above straight ahead. You can choose which content goes there. So say you don't refer to the system tray much. Use a desktop environment that places the system tray at the top of the screen. That frees the bottom of the screen (which would be in a better viewing location), for content used more often.
If you are working outside the OSHA guidelines, don't expect to setup one time and have it be perfect. Start with the general guidelines and make it as close as you can to that. From there, if you find the compromise isn't ideal, adjust to minimize the problems.