AH warplanes difference?

[Frank]

What is actually the difference between the AH warplane Prinz and Eugen. I don´t see any. And why only have the two armies on the Belgium border of the french XX Plan an mandatory attack obligation? Shouldn´t the offensive goes into the Alsace?

Thanks

[Aurelin]

The Eugen plan description mentions inner defences being ready and that Eugen is available as a leader from the start.