Excellent job,in every respect but one(maybe,possible,best to be bounced off of a stickler like "DuBois" and others).
And incidentally this is what it has to do with:
What's the purpose of the reverse taper eyes I see in old European hewing axes?
Now,i don't speak any Finnish,or Swedish(or even that much English,really...

...However,i have been looking into this very thing for a while now,speaking to many folks,some in Northern Europe of course....
SEEMS like,an "hour-glass" sectioned eye is very recent(possibly an American improvisation on the theme....(stands to reason-bigger trees,longer hafts,more centrifugal force,et c.).
SEEMS like,very roughly,the Southern Europe tended towards the (very ancient) compression eye,and up in the North of Europe-the inverse of it,Piilu being about the most radical example(btw,Piilu is what your "axe" is,not sure why folks refer to it as "Billnas"-does it have the company touchmark?).
The reason for it is that "things" were a bit different in the past,and as careful as a craftsman was,tools had a great probability to undergo great changes in moisture content(probably the craftsmen themselves too...
Now,a tightly hung hour-glass haft would almost certainly be irreparably damaged by a severe wetting,it's compression exceeding it's MOE(where compression becomes a permanent,structure-crushing damage).
Wether the conical eye would actually have a direction in which it could go,to relieve the strain.(possibly,during the inevitable wetting,a guy drove the haft loose,and as the day grew drier,just kept bumping it back in,i don't know).
In any case,i gather that at least in some of the regions of Finland it is considered faux pas to carve that neat shoulder(that is so irresistable to do,even to your esteemed Grandfather,and that you've executed Ever so well!

.
In essence,because it would disallow the adjustment of the haft further in,in case it were to become necessary...
(such a simple thought-so many words....

...)
NONE of the above is to detract in ANY way from the marvelous job you've done.My own hat's off in particular,sloppy carver that i've always been....
Respect.