Yesterday I experimented. I wanted to find exercises that might prepare kapotasana. I used the chair on the picture and also an Iyengar chair. Both have to large seats for my body. It also hurts to lie on them, also when I cover them with blankets. It feels unstable to lie on them, there is no resistance.
It's more useful to get on the knees and to walk down the wall with the hands. It makes more sense to repeat this exercise or to stay longer in that pose than to lie over a chair.
I know other preparation exercises. Hanumanasana is such an asana. It stretches the front of the hips. Being able to do hanumanasana enlarges the flexibility enormously.
Second series has 11 back bending asanas, dhanurasana included. They build up on each other. I'm searching for asanas that prepare the body for even deeper back bending asanas.
After all these years filled with forward bending asanas I love to bend backwards.