Perhaps, just perhaps, when we jelq or Uli, or whatever to acquire girth, the new growth of the tissues are very susceptible to stretching. Now, when we jelq at low erection levels or manually stretch perhaps those new tissues which may be bunched up, are easily stretched, and thus the loss of the new girth.
So just maybe un-cemented girth gains can directly attribute to length gains.
This is strictly theory and nothing more, but if we can create more tissue than we stretch, we can make a steady increase in girth and length simultaneously!
This is just my theory as I stated and nothing more, feel free to debunk at your convenience.