Multiple Audio Tracks

I know when placing visual items on the timeline that the closer to the top of the timeline, the closer to the "front" the item appears. Does the same theory apply to inserting multiple audio tracks, where the track closer to the top of the timeline "masks" the lower timeline track?  I know I can set each track to "loud", "medium", or "low". Traditionally, I place the slide's audio narration at the bottom of the timeline, for ease of locating it. Then if I have any addition sound effects they get placed nearer the top. I try to set the narration to "loud" and the sound effect to "low", but will get feedback from the learners that they couldn't hear the narration, because of the sound effect.