Yes, basically, on very thin coins there isn't enough metal to fill both dies, so it tends to be 'sucked' into one or the other leaving the
incuse ghosting on the other
side.
You also see it on such things as
Sasanian drachms, where the 4 gm of metal in a 16-20 mm Greek
drachm is trying to fill the details on 30+ mm dies.
There are some coins where this doesn't happen, such as the coins of the Rasulids of Yemen in the 14th century, where 1.5 gm of silver is spread over 25 mm or so of die, and most of them show little 'ghosting'. My theory with these is that the coins that show 'ghosting' have broad design elements (such as the
cross on your
Crusader piece) which exert more 'suction' than the
fine calligraphy of the Rasulid pieces. The piece below is just 1.73 gm and 27.5 mm in
diameter for instance.
Best wishes
Alan