You can't change the scan speed at all. Missing the beginning of transmissions is normal, as you have a scanner which may have 1800 objects to scan, other objects could be active, and the radio will be scanning for the next active object and you will miss bits of transmissions.
Clyde, N1BHH, A Know Code Amateur Radio Operator, since 1970
WQLF416 = GMRS
Pro's 94, 106, 164, 197 (2), 2006, 2015, 2021, 2055
Yaesu FT-60R, 2900R, 8000R & 8800R, Motorola MTX9250, Icom IC-735