How do some people manage to slip through the cracks with being overweight in the AF while others are separated?

I suspect your question is equally applicable to other branches as well SSgt Paul Esquibel.

An extra inch in height gives you 5-10lbs of leeway. I'm 5'6.5" so I measure 5'6" some days and 5'7" others. Changes my max weight from 170 to 175 (DoD Standards). Some folks have been known to put that extra inch(es) everywhere, like their ID card, med record etc. It's a lot easier to fight when all your documentation says you are 6'0" and the 1SG weighs you in at 5'10".... "Well I guess all that ruck marching made me shorter...."

You know whether you are close are not going in. Everyone knows their height. The week before a weigh in, cut sugars, oils, salts. Heck, all food. You'll drop 1lb/day.

"If" I were to fail that, I still get a second chance on Body Composition (Tape Test). The Tape Test can be "gamed" by increasing the circumference of the neck. Your neck muscles can be worked out FAST.

People that are "habitually" outside standards know tricks to stay inside standards when the time comes. Weight checks aren't like piss tests. We don't do them at random. We know when they are coming, so people prepare for them.

Edit: To clarify, I've never been caught anywhere near over. Been caught UNDER a couple times. Go go banana diet!

In spite of all the AFIs and guidelines, procedures, ultimately the administrative action for fitness test failure is up to an Airman's commander. There are some steadfast rules, but most of the time there are a whole lot of extenuating circumstances revolving around separation. As a rule, it is MUCH easier to separate a person with less than 15 years in service. Once you get past that 15 year mark, things become really complicated, as there is a review board involved. At that point a commander has to weigh whether not only the member, but his/her family and dependents as well, and the potential impact to them. It is not nearly easy as it sounds. You are talking about potentially taking a lifetime pension away from someone who has worked for 15 years or more to earn. Often in these cases there are medical issues, profiles, etc. that factor in as well. Administratively it is often easier just to let the person skate by and retire. Not saying it is right, just reality.