In Version 2.1.34 (beta), the new ‘Base Surface Settings’ does not properly calculate when choosing ‘Align with lowest point’. I found that I still have to go into the manual Tie Point screen, find the tie point with the lowest elevation, then change all of the pile’s tie points to that elevation. I would think that 'align with the lowest point would do this. I’m not sure what point it aligns with when choosing this option, but the volume measurement is vastly different when I do it manually compared to when I choose ‘Align with lowest point’
Since version 2.1.34 there are many improvements in the Volumes. We would recommend you to install version 3.1.23 and try to align the base surface to the lowest point. You can find more information here.