transmission loss s21

Hello,

In the lossless transmission line, e.g, CPW, or microstrip, S21^2 + S11^2 = 1,
but in the lossy line, S21^2 + S11^2 is not one.
But, does S21 contain t-line loss if substrate under metal conductor is lossless and radiation loss are extremely small enough to neglect?
then, where are the remaining losses, not counted in S21^2 + S11^2?

Sincerely,

In a lossy line the additional losses could be either conduction or radiation losses.
These loses can not be monitored by either input (S11) or forward output(S21).
For antenna there is S11 only but practically its a two port as other port is air ( not standard 50 ohm).