Without seeing the fly and the problems you are having it isn't easy to answer. Staple length needs to be similar for the dubbing to mix well. When you cut the yarn up I'd make the pieces no longer than twice the length of the hare's ear. Mix it well. a coffee grinder is my prefared method.

On small flies a dubbing loop leads to bulky flies, the way around this is to split the thread and insert the dubbing. Though for something as large as a size 10 the bulk of a loop shouldn't be a problem.

A tip from production tying might help. Tie one fly. Get the dubbing right then undo it. Take a piece of card and lay the unwound dubbed thread along the card. Mark the card where the length of dubbing extends to. Rewind the dubbing and finish the fly. On the next fly Run out the thread and dub to the length marked on the card. Then the subsequent bodies are the same. If you write the pattern and hook size on the card you can keep it and use it for all your flies. You can use the same card for several sizes of hook if you label each line with the hook size.

Several years ago I came up with the following method of tying bead head scuds quickly. I don't have any Aunt Lydia's so will use some other yarn for the photos.

Notice I've cut it in different lengths. Mixed with white hare's ear and a touch of UV white SLF for added sparkle, and given a whiz in a coffee grinder.

Put the bead on the hook and start the thread.

Tie on the shell back forward of the eye.

Whip finish and seat the bead on the thread.

Add weight if required (There is no need to mess about gluing it or anything)

Cover the weight with open turns of thread and tie in your rib.

Dub the body. Get it so you like it then unwind it.

Measure it along a piece of card. Rewind the body. Whip finish behind the bead and trim out the thread.
Pull the shell back over the top of the bead and body and secure it with two turns of rib.

Wind the rib forward until behind the bead. Secure it with a couple of half hitches and break off.

Trim off the excess shell back and give it a brush with the rough side of some Velcro.
Hope something in that helps with your problem.
Cheers,
A.