I've been carrying IWB at 3:30-4:00 for several years. I generally run my belts pretty tight (Kore Essentials and a slightly less rigid NexBelt. I suffer from OMSA (Old Man's Small Ass) syndrome and a bit of STS (Small Tire Syndrome) at 6', 190 lbs. thus the belt tension keeps things nicely above my hip bones.
When I've played around with AIWB I've found it just a bit uncomfortable standing using a Tenicor Certum 3 and definitely more so sitting in a car. When I watch videos explaining how to set up AIWB it appears the belts are not necessarily all that tight which among other things allows a bit of flex when sitting. I guess it is also possible prior to getting in a car to ease up a bit on the ratchet system (Kore or NextBelt). Am I on the right track? FWIW I'm carrying a Staccato C. Once I figure out what I'm missing I'll work with the NexBelt since the Kore's stiffness looks like it will be more troublesome.
In any event I don't think the Certum is the long term solution. I found the metal clips difficult to deal with and the snap loops don't really control the gun angle all that well.