Is the "effective wing span" reduced in a turn?
Your understanding is correct.
&quot;reduced effective wing span&quot; is just an analogy to help some people understand the concept of lift in a turn. The Total Lift is not reduced, it is just applied in a different vector in relation to gravity. The vertical lift component (in relation to gravity) is reduced and you can then imagine that the effective wingspan is also reduced by the same amount.
Banked turn (from Wikipedia)