perf12 - thank you for the link, very useful indeed! As far as I could tell my stamp passed the 5 check points.
Interesting with the 'fabricated' tete-beche pair you showed us

I guess the upright is compared to the inverted, with a horizontal line across, to indicate some proportions being wrong? Or something else? What are the marks to look for?
I did similar 'tete-beche exercise' as you did, using the stamps in your post I understand is genuine (your own stamps?) - and my own stamp as well:


It seems like none of them match 100%. But in my opinion the general trend is that the tete-beche of the forgery you showed us seems to have less portion of the neck above the horizontal reference line on the inverted stamp.
But this is just me playing, trying to understand what to look for!
Any lead - or comments
