I stand by my comment that a fitter who has a lot of experience with BD {and even better if he has a lot of foam liner experience in general}, is a big factor in this working well.
My guy used more foam than would standardly be included for both me and my daughter. Pretty painful. Resulted in zero voids, and a firmer than "normal" liner....by a touch. He was methodical in how he gave us toe room, gave me instep room. Heels are tight. 200 days into one pair, more in another...perfect.
Our fitter was one of the first to sell BD's in this country. He told me two years ago that he had foamed about 100 BD's in the prior season. Maybe more. I think he may have doubled that the next season. So, the BD is not a mystery to him. He also sells a lot of ZipFit and Intuition liners. More. Those are his go-to's.
I have heard stories that indicate to me that it is a mystery to some. I have a friend who is generally considered to be a real guru on a national basis, and he told me that he really screwed up a lot of these in his first few attempts. He does all of them in his shop now. The other techs don't. He's pretty sold on it. At first he was not.
This is a sensitive issue, as in my experience, most people have an affinity and respect for their boot guy {or lady}, and we hear a lot of great things. You rarely hear "My boot guy is real average." Just saying that thinking any good person, or experienced fitter can get this right the first few times is wrong.
Some really great fitters love them, and others are not fans. At all. That's fine. A lot of race boot guys don't like them. Think there is no need for them. I get it. Others have fitted them in 92-93mm plug boots with success.
Just saying that if you decide to go this way, it is important to have them foamed with somebody experienced with the products. My boot fitter has gallons of the foam on hand. And it sure seems like he has worked through how to get it just right based on what you need. He uses a different group of toe caps, etc.
My brother had to have a tongue replaced and foamed. He went to a well regarded guy, while out of town. He said that he was a bit familiar with the product, and would do the work, but he wasn't a dealer, and there were better options, etc. My brother thanked him, and said that he would be more comfortable with a BD guy. Found one, and all good.
The process seems really simple, but like anything else there have to be nuances to just nailing it! Probably very obvious, but had to throw it out there.