(I'm using an old image as I'm too lazy
to knock up a new one)
I missed this correlation as I quickly dismissed the letter [Z] at the start of all this, what with it being so under used in comparison to [S], and relatively easy to get rid of.
With the above pairs I got rid of the symbol with the push. So [P] went and I kept [B] for example. Following that logic I would also need to get rid of the [S] and leave the [Z]. However, the [S] symbol looks so snake-like and fits it's purpose so well that I'm definitely not going to lose it. So the [Z] remains gone.
It has made me consider if I've made the right call on the other symbols though. Is the [V] symbol more fitting than the [F]? Is the [G] symbol better than the [K]? Maybe something worth some further thought. The [V] symbol does look a little too similar to the [U] after all.
The Letter "B"
One pair where I'm fairly sure I have the right symbol though is the [B].
It looks a little bit like the female body (at least the side view anyway - belly and breasts), and seems fittingly related to childbirth. Just as the letter [M] seems to be.
Birth, belly, breast, bust, bosom, born, baby. Words relating to bursting forth. Of course, the mechanics of how we make the sound with the mouth also suggest this. As we purse the lips together and pop them out. We also have many rounded words. Like ball, balloon, bulge.
So the [B] symbol seems very apt.