Calling all experienced cordaholics!!

I have just made a new ridgeline for my BB, including a Dutch biner so it can be disconnected. My main concern was making sure that the finished RL was the same length as the original RL. This sounds simple, and I measured it several times before making the final locked brummel, but it occurred to me that burying the tail of the brummel would shorten the overall line length. I experimented on a spare piece and found that a 6" tail buried shortened the line by about an inch, enough to affect the RL. I adjusted my length and it worked out fine, but I wonder if there is a way of calculating the shortening of the line according to length of bury? I'm thinking of how this might affect loops if I were trying to make them a certain length.

Thanks in advance

Mark