Product Bundle Parent Item Valuation

I have a parent item A which have bundled together with item b and item c, item a and c are in kgs

Product A = 0.5kg of Item B + 0.5kg of Item C

the problem is the in gross profit the valuation of Product A is set to 1kg of item b + 1kg of item c.

the valution should be 0.5kg of Item B + 0.5kg of Item C

is there a way to force valuation be equal to valuation of child items?