I´ve written earlier about that but my intention was an scorched earth withdraval like Operation Alberich was.
https://en.wikipedia.org/wiki/Alberich_(World_War_I_German_operation)
On the Western front in March 1917 German troops moved back to the heavily fortified Siegfriedstellung (you call it Hindenburg Line) But the Operation started already in October 1916, they devastated the area largely shared and mined it partially. With this operation the Germans shortened the front line and retreated to a line that was much better to defend because of the terrain relief.
I have a book called “Die Deutschen an der Somme” (the germans at the somme) that contents lots of original diaries and letters. One soldier reports of an officer who painted an inscription on a toilette-door to welcome the british:
"
You crie: poor little Belgium
Poor Ireland you don´t care
Protecting culture, God and law
You brought the niggers there
I know you always hypocrites
No hear, what I you tell,
Our Germany will go to head
But you oh, go to hell!
With every good wish for a Happy Xmas
and bright New Year at Metz en C. � (Metz en Couture)
Yours Truly
Herman
" � �
At Peronne a table and chairs were put on an command post. The table was set with plates some with herring others with rats. Finally a glass of champagne with a card: “Dear Tommy, bon appetit! Do not fret, just wonder!”
All decored with a bunch of grenades, one of them a seemingly loose, so that she had to detonate when beeing picked up.
In Storms of Steel (ger: In Stahlgewittern) (For me the best book to get a first side view into ww1 battles) Ernst Jünger describes poisened fountains, undermined Streets that targeted on heavy artillery transports and the placing of time fuse bombs in the cellars of houses that weren`t destroyed already. (these bombs worked with acid)
I´m writing all this to clarify that there shouldn´t be a gain in IPCs for the allies when the germans retreat on western front.
Especially late in the AA 1914 game a situation like this could happen when more and more us troops arrive in northern france and they build up for a big push offense. Now for example if there were only a few German ifs remainig in contestet Picardy that could not be reinforced because of slow movement they may consider to go back to belgium and hold a stronger line together with units that arrived there. But before they leave they may devastate the area to slow the allies down.
As a houserule this could mean if you retread with units from an contestet region the enemy won`t get the IPC from this zone in the following round(s).