Getting UPVC beading in!!

I am just fitting some UPVC doors, and have come to fitting the glazing and beads.
I'm not quite sure how the beads should fit - there seem to be two possibilities.
The first is easy, although the seals are slightly compressed and the beadings certainly aren't going to fall out on their own.

The second is so hard I think the glass is going to break if the frame doesn't come crashing out of the wall. The seals are clearly squashed totally flat, but why else would the beading be just able to slot into that little groove?

The way I do it is as follows:

I mark the beading pieces (top, bottom l/h, r/h) before removing them, just in case the top and bottom, etc, are not identical lengths.

When reinstalling them, I install the shorter (and therefore less bendy) lengths first. The longer beads can be flexed more easily; I position each end into the corner, then push the middle to straighten the bead.

I use a hard plastic mallet to smack the beading into place, sliding it across the glass and starting at one end then working along the length. A small contact area between the back of the bead and the groove increases the pressure/area ratio and helps in opening the groove; don't try pushing the whole length of beading in in one go.

Once the beading starts to seat, the rest should follow more easily.

I agree that it can get a bit worrying trying to persuade these bits of plastic into place while you're trying not to break the glass. I'm not an experienced window fitter; perhaps those who do it more often could pass on their tips.

Xerxes,
Thanks for your reply. I take it that you agree the little lip on the back of the bead has to go into the groove in the door (ie photo 2)?
I had to give up last night, the carpet was all rucked up behind me from the pressure of pushing, and my thumbs still hurt. I will get myself a rubber/plastic mallet later, wipe away my tears, and try again.
Any other takers?

If you don't have a plastic mallet, you can use a piece of scrap wood and hit it with an ordinary hammer; just as long as the hammer head slides across the surface of the glass, it will be safe.

Done it!! But it has left me emotionally damaged. That has got to be one of the most absurdly difficult things that should have been dead easy. I had a plastic mallet, I even went to the makers and got them to show me how they do it. Tap tap, in it popped. But not for me. Still puzzled as to how it could have been so difficult. (Come to think of it, I reckon all the flexibility in the doors and frame didn't help, and they had it in a rigid frame at the workshop when the showed me.) Ah well, time will heal the mental scars. I will prevail!