A hunch -- Someone in Riau or Java is making these 'proxies' of cotengs. They get the general sense of the aesthetics from looking at tajong and coteng kerises and they make the hulu based on pictures and a bit of artistic license. If you look at the hulu from the side, it looks most accurate, but the 'properness' begins to break down when you look at it from other angles. I feel that this was the result of looking at 2 dimensional pictures, which resulted in the hulu being accurate only in 2-dimension.
Because putting the handle on a panjang is closest to the real tajong/coteng in terms of proportions (long batang), so they did it.
Attach pictures of a Sumatran hulu with similar hair motif, and as for the rhombuses with a swirl, I have a picture of a Balinese hilt with such a motif. Come to think about it, I've seen this rhombus pattern mostly on N Coast and E Coast Java and Bali hulu. I have one other hulu in my collection which I do not have time to take pictures of. I think its S. Sumatran. It has the rhombus motif. Will post pictures later.