Correct on the assumption you can't lower it because of the lower cutouts on the shield. I have one, kind of looks like there is enough opening on the lower cutouts to be able to lower one click, but haven't tried it, pretty much installed it and left it there. The older models had more of a cutout that allowed it to still be adjustable. The mfr says they changed it because 1) there was a lot of wind getting past the enlarged cutouts and defeating the purpose of having a F4+4, and 2) most customers did like I do - set it and leave it.
Even my old stock windshield I rarely moved it, and that was more to see what the difference in buffeting was. I went to the +4, got used to looking through the shield fairly quickly and now don't worry about it. There are times I get some reflection, consider it a minor annoyance more that anything.
I did add a set of Baker Air-Wings under the mirrors, makes a nice improvement for cold and warm weather riding. I would recommend them. The rest of the air-wings that go on the side and lower mounts - not so much but there are various opinions out there.
Overall - like the addition of the F4+4, and less buffetting for a passenger.