Can I dig a foundation below flood elevation outside the Floodplain?
The flood plain issues I had to deal with is more about the openings in the foundation to allow water to exit. As others have said have a Survey, my current home was in the flood plain until the survey , huge insurance jump because the lender required flood plain insurance until the survey. I am planning on an additional 3 car garage the county is the one that issue the permits, not fema.
If the county asks show them the structure is not in the flood plain, when you get your permit build to your plot plan and you will be fine.
I have a friend that built a house on poles to put the structure above the flood plain his footings for the poles were well below the 8’ or more “level identified as the 100 year level” the county only required engineering stamps on the plans, just like roof trusses require in most locations.
He has never had to have flood insurance.
Don’t bring up issues that you don’t want to deal with because as you said they go to the ultra safe side because they don’t want to be wrong. After living through several 500+ year floods he started enclosing the lower section I have not talked to him but last time I was in Corvallis the entire lower 1/2 was enclosed.
Monolithic pours are not the only way to go but you are not in the flood plane so get your permit.
Make sure you plan for drainage like a French drain under the low side with a heavy footing above that for insurance that it will drain this doesn’t have to be on the plans.
So submit your plot plan to the county and pay the fee.
If they ask , show the survey.
When approved start building and enjoy your home.