@mattison-hinelin , the answer from @KurtL1 , while correct to the extent  covered misses one critical  factor  --  the tax computation  itself to explain the  discrepancy seen by you .

The purpose of US taxation ( and not looking into Self-Employment Tax -- this is flat tax based on the net income from self-employment irrespective of the source of income i.e. whether US or non-US sourced ), the tax computation  actually uses your world income  ( US PLUS all other sources of income ) -- thus putting in a higher bracket. Then it subtracts  that portion of the tax that can be allocated to the foreign excluded income.  Therefore  you will see a difference in the tax computation when you add your foreign income.  This is despite your AGI  being computed as a difference between world income  and foreign excluded income.

Hope this clarifies  the  issue