Long ago, the Saturday after I bought my first TS55 and CT22, I drove back to my dealer because a bunch of experienced woodworkers would be hanging around. I was introduced to a famous furniture maker. He offered me some marvelous advice. In the Festool demo room that fellow had me make a cut using the demo TS55 and a 27mm AS hose, like I got with my CT22. Then he swapped that for a 36mm AS hose. What I noticed was that the larger hose was slightly stiffer and far less likely to hang up on the guide rail. Finally my new best buddy put the accessory plate on the side of the TS55. I had already been thrilled by the effective dust collection with the 27mm hose and no plate. What a difference using the 36mm hose and plate!
To get a deal, I bought one of the Festool cleaning sets which included a 36mm AS hose.
Since then I use the 27mm hose only with those Festools which cannot easily accept a 36mm hose, such as the sanders, MFK700 and OF1010 routers, the jig saws and Domino 500. For everything else I use the 36mm hose, even on sites.
As for the Kapex, I use a short length of 36mm hose. What I do is buy the 7m long 36mm AS hose. I cut 2.3m from one end, adding the connector available as a replacement part. This leaves me with a 4.7m hose useful for cleaning, until I need another Kapex hose. While I replace the hoses, those connectors last forever!
Before getting all hot and bothered about using a 50mm hose with some sort of adapter on your Kapex, consider that this can interfere with the motion of the saw. Possible it will work for straight cuts, but the whole point of a Kapex is the compound miter/bevel. A hose less flexible than a 36mm AS, especially with an adapter, will limit the motion of the saw. It also will not improve dust/chip collection.
The two permanently mounted Kapex in my shop have in addition to the 36mm AS hose connected to the dust port, a conventional shop miter saw dust shroud connected to my plant DC system. The shroud is mounted behind the Kapex to collect any stray dust/chips not caught by the dust port.