If the hand was sitting flat on the table, you would lay the transducer on the table as well. You need to put the transducer in the coronal (frontal) plane.
You can also move the hand into a “karate chop” position with a bit of ulnar deviation by placing a gel bottle under the ulnar side of the wrist, which causes the top (radial) side of the wrist to open up.
You can also get a dynamic view of the CMC joint by squeezing the fifth and first metacarpals together, which will open up the CMC joint.