3rd vs 4th edition

[Hugmenot]

Just mod it and see if you like the results.

Add a +1 modifier or whatever you feel appropriate if you believe a prepared defense in a channeling terrain should be more effective.

"Crossing a bridge" is not defined under the current rules but you could always say on which side of the river a unit is when it enters a hex containing a bridge. You might also need mods to determine on which side of the river (or on the bridge proper) is a unit that was demoralized while crossing the bridge; it may matter if they are on the far side and need to flee across the bridge and suffer the penalty again.

I am not trying to discourage you, i am all for people adding rules they like to make the games better for them, but it's not a simple task.

Please let us know what worked and what did not work if you mod it!