Yes, that must be the reduction being applied.
Keep in mind that all of the actual nutrition of the flour is preserved. It just becomes lighter.
If you still need it to be equal weight, the tag you need is [COOK_WEIGHT_DIV:2], where 2 is the number to divide by. So I would try what happens if you use 0.65 for example.
Btw, at the moment if you use the [BOIL] or [BAKE] tag instead of [ROAST], it will not apply any auto reductions.