For a monochromatic neutron beam incident on a single crystal prism, we derived analytic expressions for variations of the deflection d_cr and transmitted fraction I_O of forward diffracted neutrons, with the incidence angle ?. In the vicinity of a Bragg reflection, d_cr deviates sharply from the deflection d_am for an equivalent amorphous prism, reaching opposite extrema at either end of the total reflectivity domain and exhibits a 3 orders of magnitude greater sensitivity to q than d_am. We have experimentally observed the variation of d_cr and I_O across a Bragg reflection for single crystal silicon prisms of various apex angles in several asymmetric Bragg configurations. The observed d_cr deviates from d am by upto 27% with sensitivities |dd_cr/dq| upto 0.43 arcsec/arcsec. The results are in harmony with theory. This observation has led to the design of a super-collimator Brag.