This may be getting off the track of the OP, but if you are recording real drums, then the advice you received to record input drum levels o"f -20 to -12" are probably referring to RMS, not Peak. The standard Logic channel meters are Peak. These are going to be between -12dBfs and whereever (above) that you feel comfortable. The peak value of drums will be 10-20dB higher than the RMS value. You can monitor both values by inserting a "Level Meter" into the channel and set it to Peak and RMS. The RMS value will be in light blue.
On another note, the Logic channel meters can display their value across dB divisions that are scaled two different ways; Exponential or Linear. With the Exponential mode selected, half the meter's height is showing you on the top 6dB of the entire dynamic range. This is terrible (visually) most of the time as it make your levels "look" low. Right click on the scale to the leftmost side of the mixer to change it (see image). The image shows it in Linear mode where the top 15dB take up half the meter. If you track in this mode, you can use this scaling as a much better measure. In 24bit, if you peaks sit around -15dB or a little higher, you are plenty loud. If you can't hear it, turn up your monitor pot. A tracking session rarely has the average level that a mixed project has. As the song comes together, the average level will rise and you can back down on the monitor pot. I have mine calibrated, with some markings to give me an idea of how loud my monitoring is at any given time.
So with all that - If I'm totally off on this thread, my apologies.
[url=http://www.macprovideo.com/forum/upload/upload/server/php/savedfiles/files/mpv_42037_114133_Level_options.png] [img]http://www.macprovideo.com/forum/upload/upload/server/php/savedfiles/thumbnails/mpv_42037_114133_Level_options.png[/img] [/url]