Reaction cross sections of Tm-169(alpha, gamma)Lu-173 and Tm-169(alpha, n)Lu-172 have been measured in the energy range 12.6 <= E-alpha <= 17.5 MeV and 11.5 <= E-alpha <= 17.5 MeV, respectively, using the recently introduced method of combining activation with x-ray counting. Improved shielding made it possible to measure the (alpha, gamma) to lower energy than previously possible. The combination of (alpha, gamma) and (alpha, n) data made it possible to study the energy dependence of the alpha width. While absolute value and energy dependence are perfectly reproduced by theory at the energies above 14 MeV, the observed change in energy dependence at energies below 14 MeV requires a modification of the predicted alpha width. Using an effective, energy-dependent, local optical alpha + nucleus potential it is possible to reproduce the data but the astrophysical rate is still not well constrained at gamma-process temperatures. The additional uncertainty stemming from a possible modification of the compound formation cross section is discussed. Including the remaining uncertainties, the recommended range of astrophysical reaction rate values at 2 GK is higher than the previously used values by factors of 2-37.