If you compare, say, Reger's late Violin Sonata, Op.139 (from 1915) and Senfter's Violin Sonata, Op.26 (dated somewhere between 1914 and 1918), the kinship is obvious. However, it's difficult not to sense that the pupil (Senfter) is sometimes pushing slightly harder at the boundaries of tonality than the master - and that this is the direction in which she would go further over time, without crossing over into atonality. Senfter's music, very beautiful, seems to say 'this far and no further'.
I would think a comparison with a middle-period Reger work, eg violin sonata 4 in C or 5 in f#, which are substantially more "rebarbative" than sonatas 8 or 9, might also be enlightening...
I'm sure you're right, Eric. Thank you.