I do notice diferences between different types of capacitors with aproximate value. I could swear that there is a sweet SPOT where is more noticeable when the tone is almost totally rolled off.
It may be just my mind tricking me, but I like to make myself believe that there's some magic beyond science in the equation.
I use a old paper in oil rated at .027uf (value may have drifted) it works for me, I experimented a few different ones but always landed on this little one.
