how exactly would one make the mistake of taking a double deduction, if you don't mind explaining? i'm not sure i understand and want to make sure i don't make this mistake!
I will explain the theory and then suggest you let the tax software calculate it!
Basically, when you are moving for a job the moving expenses are tied to the income in that country -- which are also excludable under FEIE. You cannot deduct twice for the same income.
Using real numbers, say you earn $85,000 in the UK and had $5,000 in moving expenses. Your $85,000 is completely covered by the FEIE. In this instance, you cannot deduct the $85k and ALSO deduct the $5,000 -- as you would be getting $90k in deductions but only $85k of income.
So essentially, assuming you are taking FEIE, the moving expenses deduction only helps if you earn over the FEIE max. At this point, you calculate the moving expenses allowable as a fraction, so you may only get a proportion of your moving costs still.