Hi,
indeed I did not yet care.
Fact is, that the impedance of a capacitor does not follow the the rule of an ideal capcitor, because of the series R (ESR) in first place. But there still are other effects, like series L, speed of electrical signal, skin effect, proximity effect, piezoelecric effect ...
Since at higher frequencies the impedance is higher than of an ideal capacitor, it looks like it has less capacitance.
(So for me unitl now it was not of interest if the impedance becomes higher because of ESR or because of "smaller" capacitance. For me the information is important if I can use it to modify the behaviour. I can not modify the behaviour of a capacitor, but I can modify the PCB layout. With usually a much higher effect).
I guess that on a winding capacitor with its lengthy electrodes the speed of signal may have an influence of the "effective capacitor area", thus on very high frequency here indeed the capacitance may be reduced.
So in detail it depends. On the part, wiring and the frequency range of interest..
Klaus