Whether you have arrived at a fee by a wild guess or a fee schedule you want some kind of corroboration.
One option, if you keep good records, is to compare this project to a similar project. Was the fee adequate on that other one? Usually the two projects are dissimilar in some way.
Another way of checking the 'rightness' of an architectural fee is to evaluate its 'rightness' when viewed as a design budget.
This option involves doing an evaluation. It is fairly easy to 'spread out' the fee over the design phases to see how adequate the fee actually is.