Thanks for the info guys.
The offset indents just seem kinda odd to me. But like you said, all we can do is speculate. Someone must of thought it was a good idea.
Yes.Re-interpreting the lines of older designs is a complex undertaking.
Often the technical particulars of the manufacturing methods (having to do with technology of the day+region,types of ores,et c.,et c.) will morph into a specific pattern being blended with user's preference/convenience(i agree with Ernest,visibility is a likely by-product);eventually the whole becoming "traditional",even iconic for region or trade or the like.
In this particular case much depends on how exactly that eye was constructed.
I'd say that it was folded and welded in front of eye(isolating a larger mass for poll,typical for this Germanic D-eye axes).
After completing that weld the area in front of eye would be "pancaked" to an n-th degree,necessitating some attention from top and bottom.
As the welded area is refined,those arched indents would form for other technical reasons-some integrated,like fanning out the blade(for visibility) in the same time.
The off-set of indents may have to do with controlling the bending that the head may've undergone again,during the eye-welding process.
To avoid excessive rising of the toe vs heel.
And so on.That is a wild stab of Why,and having failed in a number of reverse-engineering attempts in the past i can tell you that it was probably Not like that at all!