The radial propagation of blobs generated from plasma instabilities is investigated in an open magnetic field line configuration. Blob cross-field velocities and sizes are obtained from internal probe measurements using pattern recognition. By varying the ion mass, the normalized vertical blob scale a approximate to is scanned from a approximate to < 1 to a approximate to > 1. An analytical expression for the blob velocity including cross-field ion polarization currents, parallel currents to the sheath, and ion-neutral collisions is derived and shows good quantitative agreement with the experimental data. In agreement with previous theoretical studies, this scaling shows that, for a approximate to < 1, the blob velocity is limited by cross-field ion polarization currents, while for a approximate to > 1 it is limited by parallel currents to the sheath.