How it works! From a common man.

I've always thought that there's no way in hell that both ends of the melt wire are connected in the exact same manner to the insides of the end caps.

Because of assembly line automation, you'd have one kind of attachment point with the first end cap and as the final end cap is attached, another method. 

It would be secure but different. That could account for the diode effect.
Pure speculation but what the hey?

All the best,
Nonoise

I knew this could be figured out. AND some take advantage of that VERY slight flaw. AND take it a step further.. Wrap with a tapered wire. That’s what got me..

What put me on to this was all the old bussman SBs, blew in the middle. I took me a while to figure that one...

THERE IS NO DIRECTION... LOL Never one end or the other, only the middle... The wrap failure would always be VERY close to the middle... WHY.. No direction in them, sound may not change, only the settling effect of a new fuse.

Put graphene paste on the fuse tips and CLEAN the fuse holder or swap it to a pure silver one. See what happens. Not plated, pure silver. It changes because of the BETTER conductive surfaces, on the fuse because of the paste, and holder because of the material it's made from, silver.

Regards

Either that, or the ends are a thermal mass and the middle being the point furthest from being able to conduct heat away is where the heat builds up the most.

     I decided to skip the whole fuse experimentation process and dove into, with the help of a carpenter and a surgeon friend, the entirely new, promising and exciting audio tweaking realm of head shaping and ear angles. 
     My carpenter friend has been using a very sharp wood door planer to alter the size and shape of both sides of my head,  My surgeon friend has been using precisely positioned stitches to alter the angle of both my ears in small 5 degree increments.  We began the experiment with my ears in their natural position, measured at an angle of .000036457 degrees in relation to the sides of my head, and have currently progressed to the 90 degree angle position. 
     But I know what many readers are probably thinking and please don't worry, we meticulously recorded all head shape and ear angle measurements along with my subjective sq impressions after each progressive adjustment.
     I may not look so good, my kids are scared of me and my wife left me 2 weeks ago.  But I really think we just might be on the verge of discovering something that perhaps may be slightly significant.
     Oh, who am I kidding?  This whole process is pointless and extremely painful, something on my head's constantly either hurting or bleeding, I oddly look hideous and ridiculous simultaneously and we haven't discovered a gosh darn iota of useful information.
     I've wanted to call it quits for weeks now.  But my friends are so obsessed with getting results that they now have me tied up to a chair and refuse to let me go.  Can somebody please help me?......  Anybody? 

Science sucks,
Tim