Yamaha RX-V573 Rear Speaker sensing problem

I just got this unit brand new. And start the YPAO setting. When the sensor tries to detect my left rear speaker, it says it's not connected. So I tighten the +ve and -ve at the rear, and same thing.

Then the next thing I did, I use the THX 2.0 Optimizer Blu-Ray Disc to test my speakers. I go thru that test continuously 5 times. There is audio signal on my rear left speaker, absolutely no problem

So why did the Yamaha not able to sense the rear left speaker? Any1 else have this problem?

I have 5.1 only. So I don't have the mid room speaker, and I set the rear speaker to be very back 1.

You have to understand the rear right is the same setup as the rear left, and the rear right is fine, the yamaha sees it.

surround Back Right and left

I'm pretty sure that's what it should be

good one, that doesn't make any sense. Doesn't 7.1 is the additional of those 2 x SL and SR, as such it would make sense that 5.1 is SBR and SBL.. Anyhoo, at least I know what is causing this. Guys, thank you. What yamaha plans doesn't make any sense to me, but I'll go for it

my 5.1 is mounted 12 yr. ago. and back then, Klipsch and Sony tells me to mount my rear speaker to the rear, not the side of my wall. So all these years, they have been sitting at the rear.

Also, an unrelated question, and I thought I post this, anyhoo, is there a way to tell if the blu-ray you're playing is boardcasting DTS 3/2 instead of Dolby digital 5.1, even for a brief moment on this Yamaha?