Talking with the shop owner who I tie a regular order of these for he says that they always loose the rear hackle first. To help with this he wants a small tag of tying thread behind the rear hackle, with a spot of head cement on it. This, he says, gives the hackle a little protection. If you find the same it may be an idea to try it.
I can see the logic in a smaller rear hackle if a tail is included. As his don't have, I use the same feather for both. The few I have tied for my own use have the same small / large hackle arrangement. It is however, only a half size smaller or less, just as in your example. Though these days I tend not to carry this style of fly. For me there is no noticeable advantage over a palmered fly, which I can tie much faster. This is a factor as my fly boxes are never full! Its a case of the cobblers kids being the worst shod!
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