This article brims with interesting information relating to the form Richard’s burial may have taken at Grey Friars, Leicester. It raises more questions in my mind, not least that Richard may indeed have originally been placed in a coffin, as in the accompanying illustration, but that if the grave was too small for him, it would certainly be too small for a coffin. Maybe they had to dispense with the coffin and try to get him into the grave as he was, time and so on not being on the side of enlarging the grave.
Someone else then suggested that the grave may have originally been intended for another person entirely, and thus was ready at the relevant time. This is a possibility, but who might be important enough to warrant burial near the altar? Who died at that time? Someone from an influential family. Local? Whoever it was, a small(ish) grave could be for a woman, a teenager, a slightly built man… Lighting on the right person would be a chance too far, I think. And if it was intended for a reburial, we’ll probably never know. Whoever he/she was, the grave went instead to the anointed King of England. (The only King of England, because Henry Tudor certainly wasn’t that yet, he was only the cowardly victor at Bosworth. To me that’s all he ever was.) If this possibility is true, I hope the original intended occupant of the grave still got a suitable resting place.