Recently, a subspace-constrained diagonal loading (SSC-DL) method has been proposed for robust beamforming against the mismatched direction of arrival (DoA) issue. Although SSC-DL has outstanding output SINR performance, it is not clear how to choose the DL factor and subspace dimension in practice. The aim of the present study is to further investigate conditions on optimal parameters for SSC-DL and algorithms to determine them in realistic test conditions. First, we proposed to use the Capon power spectrum density to determine the desired signal power, which is then used to compute the optimal DL factor for SSC-DL. Next, a novel adaptive SSC-DL approach (adaptive-SSC-DL) is proposed, which can dynamically optimize the sub-space dimension based on the test conditions. Simulation results show that adaptive-SSC-DL provides higher output SINR than several existing methods and achieves comparable performance comparing to SSC-DL with ideal parameter setup.