Currently the spearer can throw through a 5 pixel wall and the grenader through a 1 pixel wall in front of a lem.
Both terrain checks should start at the lem's x coordinate to prevent this.It is also possible to throw through a thin ceiling if the lem is directly under it. This is a result because the lemming is the "feet" and the projectile starting higher at the hand.
I dicussed this with namida and
we tend to only check a few pixels below the projectile to throw out extreme cases and let throwing through very thin ceilings directly at the lemming's foot be possible - an example where this is also possible would be the climber being able to climb through rough terrain sticking out at the base. So it is consistent with that.
Visualization:
So we would allow throwing through this and hitting ceilings would start if we move the upper pole a few pixels upwards.
In any case throwing through thin walls before the lem should always be prevented!Side note: The "razor's edge" trick is possible with the spearer and if you throw it at a 1 pixel thin wall it gets stuck with 1 pixel sticking out.
That is indeed consistent with builder, platformer, stacker,....