"De-coupling" coefficient?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jolyon Vater Cox by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

There is a coefficient of coupling, k, which is essentially a measure of 
the proportion of total magnetic flux which "cuts" both the primary and 
secondary windings.

Looking at the equation for secondary voltage Vout = Vin*sqrt(Ls/Lp)*k,
where k is unity in the case of an ideal transformer
would it not be possible  to use same formula with a different coefficient 
say, l, to calculate the discrepancy in secondary voltage of a real 
transformer due to the imperfect coupling -in which instance 1 would 
represent the proportion of total flux that does NOT cut both primary and 
secondary windings i.e. the "leakage" flux.

In both instances,is Ls/Lp the mutual inductance?