Hi,
sorry, I did not read your full post.
I don´t usually use that particular option, but as I always understood it, it refers to working on columns outside your range (such as if you use offsets to get values from keyfigures). If you stay in the defined range, you need to protect the division operation regardless of your settings.
You can easily give it a try, build a macro that does KF_B(t) = KF_A(t-1) with KF_A(t)=1 for the whole horizon and check the effect of the setting in KF_A.
regards,
J.