Absence makes the heart fonder... or out of sight, out of mind? ...or is it more of a per case basis?
Some people will never fade away, even when separated by a great distance, but are able to just pick up from where you left off. That makes the equation something like: number of years spent building up a bond = number of years not needing to have any form of contact to maintain, divided by 2.2 (just to make it seem not so far fetched and based on nothing coz math is involved).
For arguments' sake, this is likely more applicable should the duration not cross too many 'transitional markers', i.e. high school to college, college to working life, working life to marriage, etc. This reduces the likelihood of a change in character and/or priorities, etc - bottom line no drastic changes in the person.
then there are the 'idealistic bonds' - short term, more exciting, more entertaining friendships that need constant attention to maintain. Do the feelings of mini-disconnections attribute to the fact that the bond hasn't reached it's highest level, or does it simply mean that a person is wired that way?
I guess whichever category holds more true to you is just a reality check... a point of reference. What you choose to do about it is what ultimately counts.