Hi there, I edited your Youtube link.
https://m.youtube.com/watch?feature=youtu.be&v=7de8qTj7ky0
When I got my 120 REB, I was using a Festool 36mm hose and CTM, and was disappointed with the dust collection. It was better than previous saws but, not as good as I expected.
So I got an 1100mm length of 36mm hose, and connected it to our workshop extractor. This was a vast improvement but still not what I had hoped for.
So I changed the way I operate a mitre saw, after all these years, and saw further improvement.
Sometimes when cutting with the sub fences in place, hinders extraction, because the rubber catch hood gets squashed up, and dust goes around it, onto the saw base.
Thickness of stock being cut will make a difference too. In NA there is a hood extension like a brush that fits to the rubber hood, these apparently improve thing but, I can’t find one in the UK.
The best examples I’ve seen of dust extraction with a Kapex, are where a large rear extraction hood is fitted, and there is little or no dust doing this. Also the down draught extraction tables give great results.
Mine is acceptable most of the time but a few days ago, whilst cutting 95 x 45 and 145 x 22 there was dust everywhere.
Could you maybe do a video of you cutting with the Kapex, in the hope one of us might spot something?