These three kata are similar. The reason for the differences at the beginning of each form is according to the level of the opponent. The lower the "class" of the opponent, the less you bow. If, as you lean forward, your sword tends to slip out of the saya, tighten the saya at the koiguchi and/or snug the sword back and into the belly/hara.
 
*The slide forward on Nukiuchi, Makko, and Itomagoi are done by holding the sword, leaning back, push/sliding the hara and knees forward, then cutting. The knees should go forward, then outward. Use the power in your hips and hara. Do not bounce or jump!