IMA is like a machine and if you take out a part, the machine might not work or work as well. One part is that the extension of your trail arm has to cause the rotation of your lead arm. If you maintain lead arm support (lead arm in contact with lead side pectoral). It is very easy, especially when you loose lead arm connection, for the extension of your trail arm to pushy your lead arm through impact without causing it to rotate. Note that you must not use the muscles of your lead arm to cause the rotation. The rotation must be caused by the extension of your trail arm.