This is one of those positions that can be quite painful if practiced incorrectly. Usually, I see students do this incorrectly by trying to do too much; in other words, increasing the intensity beyond the comfort -threshold can lead to pain and injury.
To practice this safely, remember that you should feel comfortable.
Starting at the toes - I have my toes in planter-flexion however this may be too uncomfortable for you. If it's uncomfortable than simply put your ankles into dorsiflexion and elevate your bum higher. To make it more comfortable, you can sit on pillows, blocks, or anything similar you have in your environment.
Interesting note - if you practice with old phone books (i.e. sitting on the phone book) then you can slowly increase the intensity by ripping out one page per day. So if a phone book has 300 pages, you'll have depleted the entire book in roughly one year of daily practice.
Everybody's body is different. Remember to practice in a comfortable manner. When doing Reclined Hero position, as demonstrated in the video below, focus on your hips; you want to feel the stretch by way of flexing the hips as you accentuate the position by pushing the pelvis up slightly to increase flexion at the hips.