As you're working the Ionion Scale (1,2,3,4,5,6,7,8) you'll notice that some pitches, in particular, have certain characteristics when sung against chords. Some notes might create a lifting sensation or a pulling away sensation that feels like you're doing something in the opposite direction. Some of them might not come naturally to you though. This can be because of the genre you're singing in or sometimes because of the limitations of the instrument itself. For example, it is common for a guitarist to play a 1, 3, 5 of the scale and occasionally a 7. This leaves 2s, 4s, and 6s as this "sonic gap" within the chord. It's actually pretty difficult for guitarists to play these notes because they tend to fall on the same string the guitarist is already playing. A good deal of songs have guitars in them. There's a really high possibility that the notes you are singing along with within the song, are also be played at the same time on another instrument. That being said, instead of embracing the tendency to sing higher in order to get above the pitches in order to be heard; Rather use this exercise shows you where the sonic gaps are which is a good place to put your voice if you're looking to create vocal space.