I'm not aware of this ever having been applied to FTMs. It has certainly been applied to predict sexual orientation and to MTFs (Schneider HJ, Pickel J, Stalla GK (February 2006). "Typical female 2nd-4th finger length (2D:4D) ratios in male-to-female transsexuals-possible implications for prenatal androgen exposure". Psychoneuroendocrinology 31 (2): 265–9) and seems to hold.
And the right hand appears to be more responsive than the left hand, which might explain your situation, Vin.