How to pattern/sew a thick collar band for T-shirt?

[smudge]

I've been trying to create a tshirt with a thick collarband, something similar to the one in Siki Im's older collection, but cannot for the life of me figure out how to get the collar to lay flat on my chest. If I cut the collar band as a straight strip, when I sew it onto the shirt, it flops around because both sides are the same length, but the inner circumference is smaller than the outer circumference when sewn into a circle. I noticed the grain lines aren't consistent with the Siki Im collar because they chevron at the seam. I've tried shrinking the length of the collarband to almost 60% of the neck hole width(almost maxing out all ease) and there's still noticeable floppiness. Any help would be greatly appreciated!

[alyen]

I couldnt see the image you use as inspiration since it'e been removed, but try cutting the band on the bias, and topstitching after is sewn in.