It should get better over time. If you feel your at a stopping point and there isn't pain, release some of the pressure of your foot on the wall so it will want to slide lower. If you are pressing against the wall with your foot and not allowing gravity to pull the heel towards the floor, I think you are missing on some extra progress. With me, as I did each progressive rep, it would get better. I'd basically allow gravity to pull my heel to the floor until it was almost to the line of uncomfortable from a pain standpoint and let it sit there until it started aching and I needed to straighten it out. I straighten it for a minute and then slide it back downward. My heel would go noticeably lower the next time and then the next day, I would notice I started at a lower point than I did the previous day.
I'd hope the results would be similar for you.