What is the proper way to put the vario (mast)top strap in the buckle?

Is there anyone who sails completely without a knot?

I think this buckle system will slip without a knot.

If you put the loose strap-end in the sleeve, will it stay put there in waves?

My 4.3 has the same setup and i intend to set at correct length and stich it up above buckle to stop slip ...voila

Haha, Vario heads. They are still useful in adapting a sail to different mast lengths.

The problem with them are that all your downhaul settings have to be done by eye, and that won't suit some people. You never quite know where the head turban will bed down, so that means the sail luff length is no longer fixed, and recommended measurements can go out the window..

The key to getting the head turban to bed down is to make sure the gnurled slider bar can move freely. It then beds down easier in soft webbing compared to harder webbing - but the softer webbing can also wear through quickly.

So, best set the sliding bar by hand with the webbing length you want, and then tie the webbing tail off, before that first downhaul session. Once the slider has bedded in, it shouldn't move or slip again, and you can make a neater knot for the webbing tail by wrapping it around the mast tip - or some other tail stowage solution.
With a lot of excess webbing you might also knot the tail into a loop, which we used to call a 'panic strap' for holding the mast tip in waves - but this not recommended in big waves.