b5 in "7" (dominant) chords

[alez]

I'm starting to experiment with this and it's confusing me. I'm not finding it intuitive. It's like I'm unsure whether the b5 I'm about to play will sound good or horrible until I do it.

 

For example, the other day I was trying this b5 over the V7 of a blues tune (key's b2 / #1). It sounded pretty bad to me and I don't understand why, so I kept trying, but I didn't manage to make it work.

 

I'm still trying to find a reason:

 

Possible reason #1: the tone clashes with the chord.

 

I fail to see how, as this tone can be seen as a #4 (lydian dominant standpoint). Moreover, the #5 (key's b3, therefore part of the blues scale) sounded alright to me, even though I bet the guy on comping guitar was most likely playing the ♮5, which may be problematic. Despite that, it seemed to work way better than the b5. (I used the whole tone scale over V7 a few choruses to keep trying both 5ths.)

 

Possible reason #2: the tone is both

 

-Not diatonic (i.e. not part of the key signature or the part of the blues scale).

-Not a chord tone.

 

Not a valid reason, as I've seen this very scenario working beautifully before. Examples:

a) In a major tune, 11 over IVm (key's b7).

b) In a major tune, #4 over I, or ♮6 over VIm (key's #4).

c) In a minor tune, ♮9 over V7 (key's ♮6, i.e. melodic minor sound).

 

What are your thoughts and experiences with this?