Hmmm...very interesting. Aikikai people seem to have a habit of grabbing uke`s elbow in shiho-nage to keep the angle and help the throw. Not something we do in Yoshinkan, but valid nonetheless?
Personally, I usually envision making a big circle in front of my chest so that my arms are extended in a roughly circular shape, which gives tension to the shiho nage shape. However, it is true that the arm that is underneath uke`s outstreched elbow (just prior to the shiho nage compression) could conceivably grab uke`s elbow and help out, similar to what aikikai people do.
A very subtle point indeed, but was clear on the aikido3d software, and very different from what we do.
Worth a try next time...