I am not a professional, but I have been down the road of open, closed, and now custom vented molds. It is my understanding that venting or closing down has two basic considerations.
One is that if your hearing is poor in the low frequencies, your hearing aid receiver may not have enough power to build up the low frequency pressure needed to boost lows. Your low loss is not real bad, but your left ear probably does benefit from a more closed vent. You may lose bass without at least a partially closed vent.
The second issue is feedback. Having a significant hearing loss in the 3 kHz range means you will need significant gain at that frequency. That is where feedback is most likely. Your loss at 3 kHz is getting up there, and I suspect there is feedback potential. A more closed vent would help prevent feedback. Or it would allow for more gain to bring you up to target, if gain has been reduced to prevent feedback – something that is not uncommon.
What brand of hearing aids do you have? The reason I ask is that Rexton/Signia/KS8 aids have a click sleeve that is described as closed. However it is not closed, and has one small vent that is equivalent to a 1.6 mm vent. That is probably in the range that you need. I used them for a while and found them quite comfortable.
If you want I can run some Connexx software that I have which will recommend a vent size, and it would give you some idea of where you stand for vent requirements.
Edit: The other benefit of more closed venting is that it lets the hearing aid control noise better. A hearing aid cannot supply negative gain. It can just reduce output. However, with a closed fitting this is like a negative gain as the closed fitting is acting like an ear plug for noise. It can also help with directionality as the hearing aid can decide which direction you hear from, and shield you from the other directions.