Very challenging foreshortening on that position so kudos for giving it a shot! I tried to match the 3D model as close to the position as possible. The bottom plane of your bucket feels too large, which then smooshes the side planes down, shrinking the height. You lose that shape that the iliac crest and the sacrum make -- kind of like a shorthand for a flying bird -- which is still visible on an even more extreme angle. You have the sacrum positioned correctly on the bottom plane, so making sure that the bottom plane is in the correct position relative to the rest of the bucket will resolve those issues. These are really beautiful drawings, keep it up!

These are very neat! Just remember the proportions of the pelvis: The ellipse is about as wide as the thoracic section of the spine is long (especially in the fifth picture, the cylinder for the pelvis seems a bit small) Hope this helped:))