merrimack- auto set back

hello all,

For all of you who have a merrimack does anyone have luck with the auto setback?

those who do, do you pull the setback lever all the way to the left and then settle it at whatever flue opening you want? example2 inches from the right where i prefer?

its hard to tell when it is set in place.

I think i may have done it tonight as after 2 hours of burning i thought i heard a close notice, metal closing type noise, but it could of been a log falling.

any help would be great.