Gerroff!! Spell in a Siege

[Pugwash]

Hi there,

Preparing for a siege game, and wondering how the Gerroff!! Orc spell will work if applied against fortified defenders in a siege.  Based on the rules it would seem that you can target and drive back enemy units on the walls 5x1D6cm.

In this case, the original Warmaster rules state that 2D6 less dice are rolled for the defenders being driven back from a fortified position (while WMR specifies that two less hits are applied for the purposes of rolling drive-back).

My question is, can Gerroff!! target fortified units, and if so, is there any reduction for calculating their drive-back?

[Pugwash]

Answering my own question here I see that this was clarified in the Rules Update that Defended and Fortified troops are effected as normal.

For our siege game, Gerrof seems too powerful when it can rout all the cannon from the walls, and leave the enemy needing to make a dozen successful orders to restore them. So, for that phase of the game, we're subtracting 2D6cm from the result (as you would for driving back a fortified enemy with shooting), with a minimum of 5cm, which means the artillery crew flee the walls and must be persuaded to return, but not making this a multi-turn thing.

[Stormwind]

I'm 100% sure you cannot use Gerrof to automatically 'rout' and destroy a low movement enemy unit, even artillery!