Gapyrong Kim is at least 2 meters tall because his older self is the same height as Jinrang, who is 2 meters tall. Charles is also the same height as Gapyrong Kim, so he is at least 2 meters tall as well.
Due to perspective, the wall's thickness appears much smaller than it actually is. Therefore, using pixel scaling would not be accurate. Using angsize would be a better approach.
Due to perspective, the wall's thickness appears much smaller than it actually is. Therefore, using pixel scaling would not be accurate. Using angsize would be a better approach.
Edit: You should also just use pixel scaling for the whole's depth instead of angular size