....I wasn't sure either if it should cover the ridge on the wig, those hats are worn very high on top of the head, supported by some kind of small cushion. Maybe I should sit it on top of a wig without the ridge???
my only concern is how the straw hat can be attached tightly to the hair....when we move these customs, his easiest part to hold is obviously his big hat which would come off (I'm still against gluing) easily,
and since we can hardly see the bottom of his hat, his 'pillow' cant be noticed except by you and me

(this was the same problem I had when making the wide brimmed hats for my Koreans who tied a white bandana on their heads...like the pirate captain....before putting on their hats)
but if you must have this 'pillow' to get the extra height, you might as well make the pillow more visible...wrap a strip of white PVC tape around the 'pillow's edge.
as for using a wig without the ridge this would neither have the accuraccy you wanted with the pillow nor the possibility of making the hat hold tightly (only consolation is that you get the hat to sit higher)
how do you intend to hold the 3D hat down? Would using a new pirate wig with the white bandana be too inaccurate?
As for the tortoise shell helmet....a 'lacquer' black with a gold "Mon" on, will look fantastic on a mounted "Shogun", without much armor (those loose sleeves will do nicely.....can I demostrate it with a photo here?)