Hi Dave......yes, smaller clumps might help with both your problems. They are easier to pack tightly and easier to compress onto the shank keeping your thread tight.
Here's how I solve the "loose head" problem.....I spin the bunch on with at least 4 tight wraps of thread then spiral a few more wraps thru the bunch til it's in front of it. I then pull the hair back and make 3 or 4 wraps directly in front without the thread travelling toward the eye. All these wraps should be TIGHT! Don't let up on the pressure til you have all the wraps done!
Pack it and do another clump. Hope this helps...Jason
ps..sparse heads on muddlers isnt necessarily a bad thing.

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"There's always room for one more wrap of hackle"