All three postures can be modified for beginner students and advanced as well to benefit all people.
Lets start with "L- Shape" at the wall; first come to face the wall. If you need to sit with your back on the wall and where your ankle bone is please use a black to mark the distance for your legs from the wall, this is unique to your body, please respect this measurement. Move the block away bring your heels to where the block was. From here with feet comfortably below the hips, hinge at the hips and bring your palms flat to the wall keeping the elbows straight, the shoulders in the socket and the crown of the head reaching forward. This may seem like a lot of instruction but as long as it feels good, and that the hamstrings are opening the back and spine lengthening, you good!
Inverting L-Shape, step by step.Inverting L-Shape
The L-Shape is good for SO many things and is a supported inversion using the wall.
You may want to start with Uttanasana, a deep forward fold, but can be experienced many ways depending on your body IN THE PRESENT.
Modifying Uttansana is a matter of preference, I suggest trying each modification and working in a range of movements to experience the full potential of your body in the posture.
Modified version of Uttanasana in chair.
For example, sit in a chair, and come to the edge of the seat, with your legs wide inhale lengthen the spine, exhale come forward let your head and torso come as far as it can to the floor, a block another chair and rest for a few breath cycles.
Modified Uttanasana, forward folding using the chair as a support.
Uttanasana, modified without supports, but with a wide stance to allow for a wider base of support.
From a seated position you can also try forward folding with supports. While each posture compliments each other and have similar benefits and contradictions ( heart trouble, age, ability to get up and down easily) This posture can be set up and a student can stay in this reclining positing from 5-20 minutes.
I suggest allowing students to sit on a support to get their hips up over their knees. Or use a folded Mexican blanket to allow for elevation in the hips and will help with tightness.