As much as you want to push it deep inside ear canal. And it stay there forever. If you not gently pull it out bit by bit. You can accidentally detach it and dome stuck inside.
I learn how to insert it deepest as possible and learn how to pull the ear pinna so I can gently pull the receiver out from the deepest position.
Basically, Its the seal of your mold so the sound can’t escape except through the vent.
Vent also play the role in how you get the sound quality according to your ear characteristic. You either trust your Audiologist to do the ear examine for mold making process so they can decide which vent size you should use OR you have your preferred the vent size and tell them you like this vent size because it give you the best sound quality.
If ear mold not work. You send them back to fix it. Until you like ti. Which is costly.
For me, my hearing loss is so severs loss. I should use ear mold for the best result. But ear mold maker in my local shop is not proficiently enough. I can try send ear mold impression to the world class ear mold maker but its way too costly.
Oh did I mention it? for optimally you should re-mold every year? because ear canal shape is not consistent throughout yearly.
I use Single Vent Bass Dome and result is so excellent. I never look back to ear mold ever again unless I have access to world class skilled ear mold maker.
TL:DR you have to try everything. I try everything. Both mold, re-mold and ton of domes.