
The problems met with this movement come from the fact that tori find passing the arm above uke's head difficult, especially when uke is tall. And very often , instead of ending in the position in this picture, tori find himself perfectly stable with his own arm positioned as a "scarf".

In fact, you just can't pass the arm above uke's head. Using your right shoulder to achieve the movement is impossible. That muscular movement would be completely unrealistic and immediately blocked by a true uke, someone who does not execute the movement for you.

Uke's arm does not pass above his head, it is uke's head which goes under his arm. That makes a big difference.
Uke is attached to your shoulder by his grip. When rotating your body with irimi tenkan, you bring his whole right side, which holds your shoulder, in a unbalancing spiral forward down. Thus uke's body, therefore his head, pass under his own arm. He is naturally brought into the required position and there is no need for muscular effort.
Respecting that principle will allow a small person execute that movement with a tall partner for uke is brought down to the smaller person's height.
Aikido is not a sport, it is a martial art which laws (takemusu) are in harmony with the laws of the universe. Studying them allows the practitioner to understand his place in the universe. Aikido was born in Iwama, O sensei achieved in that village the synthesis of tai jutsu, aiki ken and aiki jo.
The International Takemusu Aikido Federation (ITAF) brings to the practitioner the structure he needs in order to work as close as possible to the reality O sensei MU defined. The official national representations are the guarantee of a teaching faithful to the Founder's.
In modern Aikido, weapons are hardly taught, if taught at all. In O sensei's Aikido, on the contrary, aiki ken, aiki jo and tai jutsu are unified and form together a riai, a family of harmonious techniques stemming from one unique principle. Each techniques helps understand all the others.
Peace is a balance between a human being and the world around him. The true martial art's goal is not to become stronger than one's opponent but to find in that opponent a way to realize harmony. There is no enemy anymore as such, but an opportunity offered to reach unified ki.