Ambush attacker is surprised?

[Grey_Fox]

Hey guys,

Just having a read through the surprise rules in basic (pg.393), and i am struggling with the way the rules seem to work.

Scenario- A group of soldiers has set up an ambush and is lying in wait for another group of soldiers on combat patrol (so defenders expecting trouble), defenders fail to spot the attackers and stroll right into the kill zone at which point the attackers open fire.

A roll is made for initiative which could potentially end up with the attackers becoming surprised and mentally stunned by the defenders, admittedly there is a line of text stating the GM can add modifiers as he/she sees fit for things like if one side was more alert then the other, but this seems strange to me because unless the modifier makes to roll pointless (so why have a roll at all) a chance still exists for the attacker to get stunned by their own ambush (which to me seems bizarre).

Seems the rules are made to cover the other scenario mentioned which is neither group is expecting the other at which point i think the rules work perfectly.

Has anyone else come across this? If so what was the resolution you used? Also are there expanded ambush rules in a supplement somewhere i should look at?

Thanks