I have seen quite a few threads about FL1 tailgate window problems, but no this specific one.

The problem is that when you pull the tailgate handle the window drops, but only maybe 1/8th inch so not enough to open the tailgate.

When the tailgate is pushed closed again, the window then goes back up.

The glass also goes up and down exactly as it should do on the dash switch, and the rear wash wipe works perfectly and parks correctly off glass.

As an experiment I pulled the plug off of the electric latch and then the window drops when (and as long as) the handle is pulled, but only 1/8th inch, and powers back up when the handle is released.

It seems to me that something tells the electrics when the window has dropped an inch and stops it at that point, but on mine that "something" is just physically in the wrong place because someone has reassembled it wrong.
I don't think that calibration will help because this tells the computer when the glass is fully up, not when it has gone one inch down (doesn't it?).
So where is this "something"?
Is it inside the regulator?

Think it's a count on the motor - if the cable has been replaced and not the regulator then it could screw up the count as there's too much slack or the cable is wound the wrong amount etc

I'd replace the complete regulator with a decent quality new one and go from there

I seem to have (at least temporarily) bodged it. I noticed that when you pull the door catch you can push the glass down a bit, like there is some play in the mechanism.
I looked inside and could see that pushing the glass down compresses the spring of the cable that goes into the top of the motor, and uncompresses the one on the bottom.
So I removed the whole thing from the door and moved the bottom spring round one position in the motor, which had a longer output tube.
This increases the tension on the springs a fair bit, they are now both pretty much fully compressed, but the cable does come out of the bottom of the motor at an awkward angle and I can see the cable chewing it's way through the side eventually.
Anyway the window now drops enough to open the door.
I think that I need to remove it again, and figure out a way to shorten the top, like maybe remove the spring completely or chop it down, and lengthen the bottom, or pack out the spring or something but using the first (original) position so that the angle is right.

Hmm, mine does this too, the glass drops but ONLY just enough to open the door.
You have to physically flex the rear window to get the door to shut cleanly - bend it just enough to clear the top.

Exactly the same symptoms too, it all works perfectly otherwise.

When you open the door can you shove the glass down a bit more like there is some play in the mechanism?