help with fcf and nwc

when calculating FCF, why do you just add/subtract back changes in networking capital without multiplying it by the tax rate first?

I understand the concept of NWC, increase in asset = decrease in cash flow, and increase in liability = increase in cash flow. However, a $100 increase in assets does not necessarily mean a 100 decrease in cash flow. For example, if A/R goes up by $100, assuming a 40% tax rate, cash only goes down by $40