Adjusting tube length to control dome position in ear canal

Yes, a closed dome, but i am talking about the clear tube leading from the hearing aid to the receiver.

Oh I see you have Naída BTE aid, so your using a slim tube ( thin ) or earhook and tube I wonder.
Slim tube you can’t “trim” but obviously you can do that to the tube, but how is the dome connected to that?
looking at you your audiogram I wonder why this aid, as Audeo RIC would of been a choice.

If you have Phonak Audeo Lumity then you have an RIC type hearing aid and this type of HA having external receivers which are connected via thin cables (covered inside a hard plastic tube), The domes were placed on the receiver , the receiver (speaker) is at the end of the cable (blue part in picture with 0S ) , and on the other end of the cable is a connector with smal pins.
This is a picture of Phonak RIC receiver lenght 0 , S = standard receiver

If you have Phonak Naida Lumity then you have a BTE type hearing aid, and this type of hearing aids can come with Slim Tube (about 1,5mm diameter) or thick tubing (about 3,5mm diameter)

• Hearing aids with thick tubings having an hook where the tube is mounted, The Tube can be separated from the hook and the tube could be shortened or repaced against a longer tube.
  At the ear side an custom mold is connected to the tube.

• Hearing aids with Thin Tubes have no seperate hook, and the mounting side and the Thin-Tube is one peace and can not seperated. On the ear side is an mount where you can click on standard domes.

• Thin Tubes are available in four different lenghts ( and side: left/right side ), look at the end of the Slim Tube , there you can see the specific length and side imprinted.
  see picture: blue 1L = length 1, left side ,
  Slim Tubs are available in length: 0L, 1L , 2L , 3L (for left side) or 0R,1R,2R,3R for right side)

• Thin tubes can not cut and shorten , because is is one piece of plastic.

• ask you audi or retailer about a shorter Phonak Slim Tube 4.0, 0 (zero) is the shortest tubing,

For Phonak Naida a Phonak Slim Tube 4.0 is optional , or a hook

Picture of Phona Slim Tube 4.0

Thank you very much - I realize I had a misconception about the functionality. That tube does not transmit sound but is an electrical connection to the receiver, which functions as microphone and loudspeaker.
Regarding my issue, I have changed from the closed dome to the open domes. They are more comfortable to wear and allow sound to pass more freely.

I’m looking for very short SLIM tubes for my 2019 ReSound BTE HAs. Presently they have domes and ‘slim tubes’ which are slightly too long. On the end near the ear both say "“2B”, one blue and one red. My Costco audi has none shorter, but said he would “ask around”. Anyone know where I could obtain some shorter ones??