The α-parameter is a variable appearing in the formulation of the Bray number, a dimensionless term that can be used to predict the behaviour of the turbulent scalar flux as counter-gradient or gradient in premixed combustion. However, the successful application of the Bray number is hampered by poor characterisation of the a-parameter. The results of previous laser-imaging studies of conditional mean velocities in turbulent premixed methane/air and propane/air Bunsen-flames are used to formulate an empirical description of a. The resulting description of a suggests that the behaviour of the scalar flux is dependent on the heal release parameter and the lengthscale ratio, I1/δL, rather than the velocity ratio, U1/SL.