So when you place stuff in radial symmetry in VAB you have the options to place the part 1, 2, 4, 6 or 8 times in radial symmetry.
Now, when you want to attach child parts to these, they have to be either placed single or in the same symmetry setting as the parent part.
My suggestion is this:
Allow placing of child parts in a fractional (e.g. halved or quartered) symmetry count (not sure if that's the right way to call it), if the result is a full number.
Or as a complete list:
parent 4 times -> child 1, 2 or 4 times
parent 6 times -> child 1, 2, 3 or 6 times
parent 8 times -> child 1, 2, 4 or 8 times
If this is not understandable or if anyone has suggestions on how to word it better, please tell me
Edit: remembered that 2 times symmetry for child parts on 6 times symmetry on parent parts also fits in the list