Twins' Grieving Insignia recipe question

I've been trying to get the Twins' Grieving Insignia recipe for some time now. I have gotten four of the inscription recipes (three of which are less than junk, of course) but none for the insignia.

I've done all the legendary bounties several times, the Maws more than I care to remember and Junundu Rising a couple of times.

My question is, am I missing something or not doing the right events? Or is this just bad luck with the RNG? Are the drop rates for the inscription and insignia recipes so different?

Edit: OK, well I guess I'll just have to pray harder to RNGeebuz.