Maybe not enough O2?
First I would check the Meths. Put some on a spoon or similar and light.
Should burn nicely.
You should not watch those ‘experts’ on YouTube.
If the guy in the vid used it in the forest, the floor would have coughs fire.
Those ‘wild’ flames heated up the Meths, so a nice flame.
You want to be able to sustain the flame for a certain time.
The way to do it, is to put the top part INSIDE the bottom part. And less holes.
You will get flames from the join, but it does not matter.
You need to experiment ( safely), maybe start with only a few holes. See the flame quantity.
I have noticed that the quality of Meths vary for some reason.
Plus the outside temp is a variable too.