I have to different domes like you have,one is open and one is closed,but my guy at Costco did not adjust the fitting soflware to handle the difference in coupling efficiency! should he have done that?
Yes the Audi should of programmed your HAs to what domes you are using. Go back and ask him to do it.
Thank you so much for your answer,I have had so many problems with my Ks7 and 8’s going on vacation soon and really worry about my aids and hearing people when they talk with to me.
Typically, the difference in domes going from one to the next is fairly minor. The audiologist can adjust for it without changing the dome profile where there is a difference. It may have actually been done or deemed unnecessary.
Matalie,did the differences in open dome in one ear and closed in the other feel funny?
The KS7s use the Siemens/Signia/Rexton mini-receiver 2.0, and thus the same click-domes, click-sleeves, and click-molds. (The domes they give me at Costco actually come in a Connexx-labelled package.)
These are easy to find on eBay, the Hearing Club, etc.
Thanks corona1. Yeah I got single closed domes from a Costco in the US a while ago.
Thanks ken,I just got back from Costco and he change the domes back to closed,I am getting lots of feed back,but I guess its the feed back control that is kicking in,I don’t like hearing it though.
Feedback control should control feedback. 
It isn’t doing that for you. It isn’t right and needs to be adjust or having a more power dome. You can put a slit in the more occluded domes to reduce that.
I would agree! I have swapped in my double-dome S/M with a L size many times over the months I’ve been wearing my Phonak Audeo B-Direct aids. Yes, the sound quality is a sliver different, but I make the change for comfort.
My left ear swells on a regular basis, due to exercise, humidity or even having just gotten up in the morning. While I’ve worn the size L dome on my RIGHT aid with no probs ever, I have to keep monkeying around with the LEFT aid.
When I get leaky-squeaky stuff going on (most noticeable during NON-streamed phone calls) I need a larger dome on that side. If that ear canal swells up tho, it gets red & painful jamming the L dome into the ear canal. I only developed this problem in the past few years.
Oh well. Old age SUCKS. And if this is the extent of my discomfort, I am very lucky. 
I have different size domes. Not a problem. My hearing is pretty asymmetric, so I’ve even used an open dome on one ear and closed on the other. Of course, you need to handle that int he programming.
An earlier post by Doc Jake taught me that there should be programming adjustment to the aids when there is a change in venting. Was that done?
@Um_bongo remarked that it wouldn’t be a serious difference but one to address next visit.
As to the topic: yes, two sizes aren’t unusual. I use a large in the left and a medium in the right.
I have not had good luck with the fitting at Coscto’s. I have went back to my old back up’s and going to try Zip hearing next,I had heard some good things about them and will try and see if they can help me with my hearing problems and a good fit for a hearing aid for me,I was going back and forth to Costco’s every week,sometimes twice a week,got really tired of all of it.