For the sharp eyed the first photo with Naca5 on Spendor’s does indeed have the leads reversed. I grabbed a couple images and that particular one the amplifier being used (Jadis) reverses phase. Another oddity that was clearly audible.
I believe Nordost and others have put out bulletins discussing the various options for bi-wiring and use of jumpers. I found the diagonal arrangement to provide me the best sound. The great thing is this is a potentially no-cost upgrade
Certainly easy enough to try the different options and determine which you prefer.
When I used speakers with jumper plates I was advised by a speaker design engineer at Linn to put the positive to the highest frequency unit and the negative to the bass.
I used this as advised all the time I had multi connector type speakers.
When I read your post … I too was “Skeptikal” … but just tried it … and like it 
I use NAC A5 jumpers on my ProAcs which are fed with NAC A5 from my Nova.
I suspect that ProAc & other manufacturers supply their speakers with metal jumper plates (or similar) as: -
1 They feel they work as well as cable or, more likely,
2 They have no idea what speaker cable is going to be used in the owners system so can’t supply the appropriate jumpers & just supply a ‘one size fits all’ solution.
Great stuff I’ve always used this method and there is no cost to try and much pleasure to be had.
ATB. 
I now have Kudos speakers with single terminals. 
Edit
Here is a post from a now defunct site that explains it.
“Exactly the way a single wired passive speaker should be connected. I have been demonstrating this to staff recently during some tune-dem refresher
courses I have been running. Majik 109 with positive connected to tweeter and negative connected to bass compared with both connected to bass. It makes
a surprisingly large difference to detail and clarity.
The reason for this (if you are at all bothered) is that you always have the same impedance between the amplifier output and any drive unit in the system (the
length of speaker cable plus one full link plate). It is also important that the negative wire goes to the bass negative as it gives the clearest path for the back
e.m.f. from the bass driver to be sunk back through the amplifier, reducing its influence on the other drivers in the speaker.”
Phil Budd (Philbo) LINN STAFF
Hobbit loudspeaker designer
Well … all I can say is … who knew 
Switched my Response D2 from LF terminals via HF terminals to this … and found it both clearer and a more relaxing presentation.
I may have to empty the dishwasher and “do the swop” now 
I went diagonal after reading a few forums, and its certainly quite a bit better. As the Linn guy says, more clarity and tighter bass, not a subtle change on my speakers.
Swopped and rebooted on my DSM/PMC’s. Interesting, it does sound different indeed.
Gotta love a free tweak.
If one really does hear a difference then it suggests your jumpers aren’t up to scratch
Tried it and sounds better to me so happy.
NACA5 and chord signature jumper leads here.
Any science to back up your assertion if you hear an improvement there is an issue with jumper leads?
Well I would have thought that if the jumpers were completely ‘transparent’ then electrically speaking it should make no difference which speaker terminals you use
I had those same Totem jumpers with my Tribe Towers. They are junk and worth changing.
Okay thanks for clarifying and also to Skeptikal for sharing 
.
The issue is in your assumption, not the conclusion. Surely no wire connection can be perfectly transparent.
Mark
Actually, I was bothered about this! Well, intrigued, at least. Thank you for this, @Skeptikal - that explanation makes a lot of sense, so I now can be bothered getting on my hands & knees and trying this out for myself.
Mark
I’m Skeptikal about this.
Won’t the crossover inductors, capacitors, resistors……… create different impedances between amp and drive units. 
Although, when I get my amps serviced I’ll definitely be trying it.
Don’t be Skeptikal just try it as a free tweak. 
The guy that designed the speakers is qualified enough to listen to.
Give it a go nothing to lose.
I was Sceptical, and my dealer on several occasions had said to use the LF plugs, but I tried diagonal and it’s better - no doubt. To the extend that I’m slightly bemused I didn’t do it earlier.
