Here's a screenshot that everyone will understand the trigger_hurt high window correct.
The green lines are the trigger_hurt. It's only 2 units thick. You shouldn't touch it too long, though.
The yellow lines are the area where you could move without any problems. As long as a player doesn't touch the window/trigger_hurt (green lines), it shouldn't be a problem to sit high for the whole map.
I've tested a few more things today. It seems that the game just saves the damage of one round, but not across different rounds. So the only possibility to die is sitting for more than 100 seconds inside the trigger_hurt (green lines) in the same round. It's not a perfect solution, but I think this doesn't happened that often.
The ent file is now online at our public server, too.
I've attached the ent file.