To make a pair with the incR, you need a left lifted increase or incL, LLI. There is much more documentation now than there was when I was on my search for the pair to an incR/RLI. I spent some time figuring it out on my own. Maybe it was out there, but not in any of the reference material I had at hand.
Left Lifted Increase, incL, LLI
I set out to figure out how to get the same effect in an increase that sprouted from the left. Today, if you look up left lifted increase you will find it. Once I’d figured it out, I dubbed mine incL, to go with incR.
It seems logical that you would just go knit into the stitch below the last stitch on the right needle in the same way. If you try this you will find that all you create is a second loop on your needle that isn’t really connected to the stitch–because you just made the stitch on the right needle. If you were to then work that second loop (and you would have to work a knit on the WS or go into the back loop to make it work) you would end up with a hole because it isn’t connected to the row below.
To make the lifted left increase to match the incR, which is coming off the left needle, you need to go down to the row that would align with that. This is now the row below the row of the stitch just made. This is on the right needle, so needs to be picked up with the left needle. It seems more awkward, but once you get the hang of it, it really isn’t. You will know immediately if you knit into the row of the stitch just knitted. There will be a double YO on your right needle.
Finessing the Left Lifted Increase
IncL: This increase goes a little differently. You can insert your needle into the stitch from the back or from the front. It is a more difficult to go into the top of the stitch in the row below from the front. Your right needle is in the way and there is less tension because it is in the row below. It is very easy to go in from the back. If you go in from the back, the increase needs to be knitted through the back leg from the left needle. If you do that you will have a lovely left leaning increase. If you pick up from the front, simply knit the picked up loop.
IncLp: This is easy to work. If you pick up from back to front, you will need to purl into the back leg, but it is right there and easy to do. I did a series of incLp in my swatch, going in to the stitch below from the back and the front, and there is no visual difference if the purl is worked into the correct leg of that lifted stitch.
I’ve done a lot of increases in my swatch and you can see that it is not distorted at the bottom. There is always some pulling upward, but this is smooth and fairly minimal. This minimal distortion to the fabric is the reason this is the left lifted increase (incL/LLI) and it’s pair, the right lifted increase (incR/RLI) are the increase I most frequently use.