Limited support
This feature is only present in Portal 2: Community Edition and Portal: Revolution.

mp_bot_fling_trail_kill_scaler

🟦 Executable on Client

mp_bot_fling_trail_kill_scaler <value>

The scaler that determines how close to a portal a player has to be (when flinging towards it) before the trail turns off

Warning:

This is a cheat command and can only be used when sv_cheats is set to 1.