I've only taken the helmets where I'm pretty convinced that the standard Prussian Wappen is original to the helmet. Measured with a tape along the Wappen from the cross on the head to the tail feathers, +/- 1 mm measuring inaccuracy

:
Year - Maker - Size - Wappen - Height
1896 - Unknown - 56 - 11.0 cm
1906 - Unknown - 55 1/2 - 11.0 cm
1910 - Rudolf Wiemer, Mülheim-Ruhr - 55 - 10.8 cm
1910 - E. de la Croix Nachf. Berlin - Unknown - 10.8 cm
1916 - Wilhelm Becker & Co? - 55 - 10.8 cm
Loose Tombak Wappen - 10.8 cm
Loose iron Wappen - 10.7 cm
As all Wappen seem to be 10.9 mm +/- 1 mm in height, I conclude from this very limited data set that there is only one standard Prussian Wappen size.
If you have very large or small Prussian helmets please measure the Wappen height so we can (dis-)prove above conclusion.
Regards, Lars