First 1 turn is always though both hole there is no .5 turn.
Also if the inductance of the winding is not high enough you get a low
frequency cutoff. Changing the ferrite to higher mu (43 to 73) will help
but more turns would have as well. The cost of higher mu ferries is
higher loss at higher frequencies.
The coefficient of coupling is never 1, it may be very close.
Typical for a binocular core is around .997 or less depending
on how the winding is structured as well as lead lengths.
The latter contribute leakage inductance that degrades
transformer action.
Allison
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