I also say with backbends, you have to be cautiously bold. Not carelessly bold. You have to descend to the dictation of the spine. You cannot command from the brain to do the poses. As you play with a child, guarding the child from injuries, similarly you have to play in backbends, guarding your spine.
That's the beauty of backbends. Emotionally we can never be disturbed, for the emotional centre becomes an extrovert. When you do Viparita Dandasana, your head looks backwards, but your conscious mind stretches everywhere. Study by observing how the mind gets regulated. You not only know the freedom in the spine, but also the freedom in the spirit.