Have a look at the costing sheet and how these interact with production costing. Essentially fixed costs are that no matter what quantity you make, whilst the variable moves with the quantity per as it is a unit.
It will all depends upon how you have defined the indirect elements and how the calcualtion is created - are you seeing any indirect costs or seeing them but they do not alter - what is the indirect cost type node set to - surcharge or rate?
Those are defined as surcharge with 10% in the costing sheet.
I have 1 bom with cost $120:
( Material cost: 100
Fixed cost: 10% = 10$
Variable cost 10%: = 10$ = Total cost: 120 )
Now if i produce 2 Boms then cost should be $230 but showing as $240.
I think the fixed cost should attach only once for one single BOM but attached twice for every single Boms. It seems to be variable cost same as fixed cost.