I wouldn't worry too much about it. The math doesn't even make since. The din threads go into the adapter brining the part that attaches to the yoke valve within the same range as a normal yoke connection. Maybe a half inch added in there if anything. Considering the amount of times you will use it. I would suggest you don't spend the money on a yoke kit or the fee to install it. A trial in a pool may be in order. Let me know the results!
I agree with this opinion.
I have used a DIN to yoke adapter on a week long trip, not a Deep6 adapter, though it looks the same. No problem. Depends a little on the configuration of the first stage, but even if it sticks out a bit and hits the back of your head, just lower the tank a very little bit in the tank bands. Should be no issue, IMO.