The way you just described would put the bottom of the speakers forward and the tweeters back slightly, because they are overall below you on the desk. Even though the tweeters are in line with your ears, you are promoting the lower frequencies arriving at your position first. The plane of the front of your speakers is not vertical and horizontal in the real world. I would imagine, because the way the sound bounces in your room is different than mine, that you might be receivng an image in which the low end slightly masks the high end. Your decisions will be based on the fact the the ear is getting the low end information first and responding to that. Also, you stiill may have to adjust your acoustic in your room to deal with the angle the monitors are overall pointing in the room.
The whole idea is to create a large square sweetspot, with as much depth, height and width as possible. You are trying to deliver the best spread of frequencies, from low to high, that your monitors can deliver to your listening position. You are also trying to get the best soundstage for placement of instruments and most importantly to hear the frequency overlap characteristics/problems of the instruments and voices.
Another consideration is depth. How accurate and how loud are reverbs? They tend to push things back into the mix. If you have to crank your reverbs to hear them and then notice they are excessive on other speakers, then your sweetspot may be lacking, or your monitors just aren't providing depth. Or, the placement, spacing and real world planes are not maximized for your listening position. Another issue may be that you can hear the reverb, but it does not accurately push the sound back into the mix. Either the speaker positions are off or your monitors are not creating an accurate image. Possibly both.
So, I would recommend, getting some speaker stands to elevate your monitors so they are vertical and horizontal in the real world with the tweeters at ear height and the monitors turned inward toward your listening postiion both aimed at a point 12 inches behind your head.
I actually measured the distance from the back walls that my speakers sit in the room. adjusting my desk so they are the same. I then measured the exact position of each monitor corner in relation to the other one. I have them precisely horizontal and vertical in the real world and turned inward exactly the same, used string, to a point 12 inches behind my head.
The result was a wider sweetspot. I think I have buried the issue at this point so I will sign off. Good luck with your imaging. It's one of the most important things you can do along with treating your room.
