The Modified Chlorophyll Absorption Ratio Index (MCARI) algorithm in SNAP is:
MCARI = ((red_factor2 * red2 - red_factor1 * red1) - 0.2 * (red_factor2 * red2 - green_factor * green)) * (red_factor2 * red2 - red_factor1 * red1)
For Sentinel-2 the formula is: [(B5 - B4) - 0.2 * (B5 - B3)] * (B5 - B4), where (Central wavelength/Bandwidth): B5 = 705 nm (15 nm), B4 = 665 nm (30 nm), B3 = 560 nm (35 nm)
But I have noticed in ENVI the MCARI is: