Your initial post was ambiguous. It made me think you were referring to under-inking of the stamp image. From your later post, I infer you were talking about the overprint.
Did you measure the length of the overprint? It, not only, looks much thinner than the examples posted by lithograving. It looks shorter, but that might be an optical illusion.
I agree with you that the difference in the type of the overprint has nothing to do with soaking. I also doubt it is a question of under-inking, the quality of the overprint is terrible.
Considering the remark made by lithograving:
Quote:
There are no variations in the thickness/thiness of the overprint
script as per the Austria Netto Katalog.
It raises the question whether the overprint is genuine.