Both transmission and reflection of a short light pulse are considered for a double prism system in the geometry of in-gap refraction with an account of material dispersion. Within a frame of linear optics and Snell refraction law, we revealed the effect of a 'negative dispersion' regime close to the total internal reflection. A narrow area of parameters (wave number and angle of incidence) in the close vicinity of the total internal reflection is found to possess specific properties for the refracted field. A resonance excitation of leaky waveguide modes enables to extract the refracted field from the gap efficiently and inspect various transmission regimes. Analytical consideration and simulations demonstrate an appearance of advanced pulse in the transmitted and reflected waveforms, with the temporal shape depending on a number of modes enclosed in a spectral width of an incident pulse as well as the existence of elongated precursor within a gap.