Definitely open mouthed. Like yourself I took John's advice and used a relaxed closed mouth and then had to get them redone because one side was too loose. If I was to do it again I'd adhere strictly to the UE Guide for the best opportunity of getting a good tight fit first time.
John - CA Office - The Official LiveWires - Custom Fit In-Ear Earphones
Please ask the hearing professional to take the impressions to at least the second bend in the ear canal. The impressions should be taken with your mouth opening and closing several times while the impression material is in the ear.
Earl - TN Office - Fidelity Custom Earphones Official Home Page
Have a set of impressions made. Using silicone impressions material and a "bite block". A bite block is usually a sterile
cotton or hard foam pad placed between the upper and lower teeth, to hold the jaw open about 1" while the impression
material cures. This is an important step as the soft cartilage just past the first directional bend, increases in volume (size)
when the jaw is open. DO NOT open and close your mouth while the material cures.
BELOW ARE THE INSTRUCTIONS FOR THE AUDIOLOGIST
Observe recognized procedures for otoscopic exam of the ear and be certain to screen the client's ear canal for contraindication
*Insert an oto‐block slightly beyond the second directional bend.
*We require the entire outer ear and down to the second bend of the ear canal.
*Use a “Bite Block” to hold the jaw open about 1 inch while the impression cures.
*Use only silicone impressions material. Impressions will not be processed from powder and liquid type materials.
*Syringe the impressions material into the ear.
*Be sure to fill the canal up to the second directional bend and fill the concha completely.
*Provide ample time for the impressions to cure completely.
*Impressions must not contain cracks, ripples or voids.
*Carefully pack impressions in a crush resistant box and add the Information Form. One for each client.
I will definately go for the open mouth.
I think after now reading all this and now confirming that my original impressions could have been done to get a better seal, if I send them in to get them re-shelled I may aswell get the upgrade and kill two birds with one stone.
Thanks for the advice