High eyeheight in a low room
When raising the eyeheight over the default value in
jDoom, the eyeheight doesn't increase, only the weapon
is moved down slightly. In jHeretic and jHexen it works.
Using several times "sub player-eyeheight -20 force"
makes the player eyeheight raise very much. Then
using "sub player-eyeheight 20" or some other values to
make the eyeheight drop to 54(which feels more
realistic). Then the eyeheight is really 54.
Now that the eyeheight is 54, and sector height is low,
about 56-64, player can see through the ceiling into sky
or into another room.