2 ways to calculate residual income. 1 through NOPAT - $WACC which is equivalent to EVA while the other one is through NI. Projecting the NI and adjusting from it the equity charge. If interest expense is treated similarly i.e. dollar amount & percentage, then both equations should yield the same RI.

Interest Expenses treated similarly means that the interest expense which is deducted from EBIT is the only interest cost and it also reflects in WACC then RI should be same under both methods. If there is some interest income then both equations might not result in the same RI.