If you put too much upward pressure on the knuckle with the jack it jams the strut tube in the cup. So just enough to hold the knuckle up. Also the top 3 nuts on the strut mount inside the engine bay need to be loose.
With the nubs lined up in the cup/slot in back. The way I did this was grab the strut body in one hand, and the brake disk and/or caliper in the other, and twist the strut back and forth while shaking the disk or caliper back and forth. The strut slides in a bit, then you lightly jack the knuckle higher. Repeat several times until you can't move it anymore. The strut assembly has to be loose at the top to do this the clearance inside the cup is so tight.
I will be under the car again today (doing downpipes I hope) and will measure how much strut is sticking out under the knuckle.