Assume the AC voltage has no loss. The loss due to capacitance. We are just talking current not voltage.
Think about flyback in continuous mode, where the DC is a major part of the current and AC is small. (big time continuous)
It is safe to think the DC is traveling through all the copper and the AC is on the outside the wire.
In other areas we often take a complex waveform and break it up into it components.
....90%=DC, 5%=1mhz, 2.5% at 2mhz, 2.5% at 4mhz.
Then tread each "frequency" or "harmonic" as its own thing.