This has been an issue for a while now. Ever since the clipping changes it is no longer possible to decrease the player's z-position to simulate crouching, in particular, this breaks the 'slide kick' feature found in the AMC TC.
The intention of the slide kick is to allow the player to slide through tight gaps, slightly larger than the ones intended for the shrinker. This used to be done by increasing the z-velocity of the player so he is pushed downwards.
In the latest revisions, not only is it no longer possible to move players through these tight gaps, it is also not even possible to move him into vent-sized openings this way. (at least without using excessively high values)
Is there any other way to achieve the desired behavior in CON? I've tried decreasing the y-repeat of the player but while this does allow passing under tight gaps, it comes with all the undesirable behavior of shrinking.
