Perceived Volume of Mix

I mixed two songs for the same album.  One is a full country band.  The other is a ballad with just voice, finger picked guitar, cello—and very light bass and drums that come in midway through the song.
 
Both have master bass compression to keep the level maximized accodring to the master level meter.
 
The problem is that the ballad with light instrumentation sounds louder, possibly because the arrangement is so sparse that the relative level of the vocal is higher than on the full band song, even though both haved similar overall levels.
 
Now my question: do you normally mix a ballad with minimal instrumentation at an overall lower level so that the voice sounds consistent with the full band arrangements?  I could do that, but I don't want people reaching for the volume to turn up the ballad when it starts with just a finger picked guitar.
 
Thoughts on best practices?
 
 

Thanks, Chregg, I will check it out.

Just using arbitrary made up numbers for conceptual purposes, suppose your overall mixes both have a level of 10.  Could it be possible that in the full band arrangement, the vocal volume level is 3 of 10 whereas in the ballad it is 5 of 10?  Maybe the user perceives the ballad as louder because the vocal is taking a larger share of the available headroom.

To put it another way, would it make sense to set the overal level by looking at the vocal level soloed and then build around that?
 
By the way, it looks like your Soundcloud link is broken, but I would like to hear your stuff. 

RMS levels will be vastly different in the 2 songs , for me it is best just to do this my ear. Getting the vocal levels matched
  is a good place to start. Put the song side by side and play the songs back and forth also listen how they transition. 
Adjust to taste,