This is a great question

Unfortunately, the Brooks Act nor any other legislation codified or created a list of what services should be included and what services can be excluded for the 6% statutory cost and fee limitation. I won’t bore you with the details but a number of Comptroller General decisions from the 1960s set some general guidelines regarding what services might be excluded from the 6% limitation.

The key is if the services are an integral part of the preparation of designs, plans, drawings, and specifications they are included. If not, they may be excluded.

A search of the GAO Redbook, Fiscal Law Deskbook, Contract Law Deskbook, the DoDFMR (which is not user friendly at all) and finally through Army and USAF pubs to find a more definitive source of guidance revealed little more than what DFARS states.

However, ARCHITECT-ENGINEER CONTRACTING IN USACE, EP 715-1-7 (Appendix Y on pdf page 193) provides examples of services that may be excluded. Here is the link

https://www.publications.usace.army.mil/Portals/76/Publications/EngineerPamphlets/EP_715-1-7.pdf

I won’t cut and past the list here as it is rather lengthy. Interestingly enough, it is very similar to the guidance found in the Department of Veterans Affairs Acquisition Regulation Supplement (VAAR) 836.606-71(c). Other federal agencies have supplemented the FAR with similar lists, but an exhaustive search was not accomplished.

Again, while my search of USAF pubs did not reveal anything, your CE Squadron might be able to guide you to where it resides.