focus stacking for landscape? Possible? How?

[nma]

Hello,

I am trying to make a go of ML for my landscape focus stacking.  I am having problems setting the focus endpoints.
In landscape orientation, I want to set focus at bottom edge as start and end focus deep into the image. This could be top edge but usually about 3/4 to top. I can only focus in a small recatangle in the middle of the frame.

Is this possible adn useful in ML?

Thanks