I don’t have much experience, having just got my first HA’s and my first earmolds in the last few months. But I had hard silicone molds made by ReSound. They actually seem to be made just a tad larger than the dimensions of my ear canal and were made from a 3D scan of an impression (injection of silicone molding plastic). When properly inserted, the outside seems to be a few mm below the plane of the concha area surface and the molds go 15 to 16 mm into the ear canal. So the first section of the ear canal is cartilaginous and somewhat elastic - so I seem to have to stretch my ear canals just a bit to get them in (I pull up and slightly out on the upper back portion of my ear lobes both on inserting and removing the molds and I do it by an off-and-on tugging motion since I’m unsure exactly how much tugging is best). Nevertheless the tension of my ear canals gripping the molds holds them rock steady in place. The small plastic string with a bulb on the end used to pull them out has to bend a bit, too, against my ear lobe when the molds are inserted to perhaps that slight pressure of that plastic also works slightly like a concha lock with its slight springiness helping to press the mold against the other side of my ear canal and creating additional friction. With domes I had concha locks that couldn’t seat properly in my “antitragi,” since I have little or none but strangely, I have never had a problem with either domes or molds slipping out.
I have attached a picture of my right ear mold. The red arrow is pointing to a notch and protrusion in the upper part of the mold, present in both molds, that may be designed to catch the mold when inserted on the crus helias arch of the ear lobe that crosses the lobe from front to back just above the concha area, either that or to keep me from trying to insert the molds too far. Haven’t figured out which.
Image of crus helicis (“crus helias” is Dillon terminology in 2012 HA book)
https ://en.wikipedia.org/wiki/Helicis_minor#/media/File:Slide3COR.JPG
By Anatomist90 - Own work, CC BY-SA 3.0, File:Slide3COR.JPG - Wikimedia Commons
