I have used SRAM groups except Red.

So for the other groups... In the smallest cog, the right lever usually is limp indicating it is at the highest end (like a empty trigger, if you will). Just alot of play to let you know there is no more, Double click will go into second cog.

I just installed a SRAM red right shifter, keeping the rear Apex RD, and now it is different. In the smallest cog if I push the lever it would immediately make the RD move towards the second cog, the first audible click will latch on the the second cog. If I do a double click it goes to the 3rd cog.. so, it seems kind of confusing.

All I can think is that this is the zero loss feature, that there is no more limp trigger? Or that, the first click while in the smallest cog is inaudible. Did I mess something up?

On the other hand, the other extreme which you might encounter is the shifting down to a smaller cog when you get up to the biggest cog and forget and attempt another shift.
Inherently, its a limitation of the 'double-tap' ergonomics, can't get away from it unless SRAM adds some indentation to indicate the end points of the cog stacks and prevents miss-shifting once you're at the limits.

Different experience here. On smallest cog, there is a little bit of play before the first click. You pretty much know you are at the limit and the next click will move you to a bigger cog. On the biggest cog, you have a ghost shift where it will click but not move the rear d any further (into the spokes).

thinking about it, on the smallest cog, the first click goes to the next cog

it did take a bit of geting used to

Di2 is where its at:) I'm glad I got rid of my red group a few months ago!

In the smallest cog the first click will always bring you to the next one, but your right there normally is a little bit of play (at least in mine there are). Maybe your rear shifter cable has too much tension in it? Or may not be seated in the shifter completely. Just a thought.

I think you are right, I must have been confused with the non-zero-loss group, they must have just go on 2nd cog with one click. But I have the habit of using that play to tell I was at the end, so with the zero loss I immediately confused myself. Just took a bit to get used to I guess. I was always listening for 2 clicks when it is probably better to use the throw distance to judge.

I unpinched the cable and pulled on it while clicking the lever to make sure the indexing is reset and also made the tension so loose it wouldn't shift.

Di2 kept going through my head as well... but I am happy with Shimano mechanical group, I found it easier to shift when I am completely exhausted on a climb and lost my other motor skills.

Agreed it does feel different than rival or apex but I think Red has the best feeling shifts considering Dura ace too.

It does feel more precise due to the zero loss. Do you need RED RD to get best results? I ordered a force RD to replace the Apex RD. The quality control is poor on the bottom tier SRAM. I had alot of down time doing warranty or replacing due to defects -- they feel really cheap.

I've got a rival RD on my commuter with Red shifters. Supposedly the only difference between force and rival is weight due to lighter hardware. I'd contend the feel of the shifts is pretty dang close to the full red on my normal bike, close enough that I'd wager that cabling and adjustment makes a bigger difference.

IMO, a full rival group with red shifters is a heck of a group for the price.

I'm not sure about this but I thought the red RD had a better spring inside it making the shifting crisper than the force or rival. However, I have used a force Rd with red shifters and it feels pretty darn good too. I would say the majority of the "feeling" comes from the shifters.

Hmmm. My bike's put up for the winter so I can't check off hand, but I don't believe I have that feature with my Red front shifter. I believe it needs a normal double click to get from the smallest cog to the next one larger. At least I've never noticed any different shifting there compared to all the other downshifts in the rear. I wonder if your outer stop needs to be backed off just a tiny, tiny bit? It's been a while since I installed my RD, and I can't remember if the jockey wheels are supposed to be right centered with the smallest cog, or a little bit outer or inner, but you might double check the Sram instructions on that.

And I think I would have noticed because I definitely noticed a fairly common issue on the other end of the cassette - before I tweaked my inner stop just a little bit, I'd often accidently shift off the largest cog to the next one down, and I was annoyed with this (even though I could avoid it by simply remembering I was in the lowest gear back there). After the little bit of careful tweaking, it now gives me a ghost click and stays put.