ok - so I have a bit of experience with this. I just completed a mini galaga style cabinet (
http://forum.arcadecontrols.com/index.php?topic=68683.0). Here is a pic:

As you can see, the monitor mounts straight up. This cabinet is true to scale in the fact that the bezel is properly sized and was reduced to 25% of it's normal size, same with the sideart and marquee.
Before I built the mini bartop cabinet, I had considered a mini cabinet that had proper proportions. I made a mockup with cardboard. Here is a pic:

After I built it, I could see the monitor would not really be visible, and thus the game would be more for looks than playable.
The monitor is a 10"/9" viewable CRT monitor. So I went with the more playable but not 100% accurate bartop. Your call! What size monitor you talking about using?