FWIW, before posting the original discussion, I had spoken with ZAC regarding this issue. The 650 wing is set to address lighter engines and the easiest way to lower the nose on the XL and 750 is to raise or lower the horizontal stabilizer leading edge.
You don't have to trust me, call ZAC, but it goes like this. To lower the nose on the XL, raise the leading edge of the stabilizer up to 1 degree max, it would be a good idea to start at .5 degree.
On the 750, the airfoil is inverted, so you would lower the leading edge up to 1.5 degrees max, .5 degrees at a time.

I also believe that the XL/650/750 were designed to fly level in cruise configuration. The top longeron is the reference point, XL/650. and the horizontal stabilizer is set parallel to the longeron. Before you can impose the flying with flaps creates drag logic, you have to start from level. It could be that using flaps to level the airplane reduces the drag created from flying at a pitch angle other than level, thereby offsetting drag created by using the flaps.

Went out today with an inclinometer and found out I was flying nose high because I wasn't sure what level was, duh, I don't have a pitch indicator. Flying level raised my left wing and reduce aileron and elevator trim, go figure. It should also improve efficiency. I'll be installing an inclinometer for reference.

Obtw, I deleted the other discussion.

Final point, in the Experimental Amateur Built world, we are the manufacturers of our airplanes. ZAC provides the material, but we can do whatever we want to do before and after inspection, the FAA doesn't care, we're experimental. We have no limitations, so don't squander the opportunity to improvise.

Innovation is the by-product of experimentation.