I can sometimes kind of read ahead 1 bar, but it takes an intense amount of effort, reading two bars ahead is beyond me.

I am very quick at reading the notes that I am currently playing, pretty much at temp, though unusual note durations (strathspeys, slurs over the beat) give me trouble, as do some accidentals, especially in unfamiliar music.

Good luck on reading ahead, if you figure it out...

I'm not sure why anyone would want to sight-read two bars ahead, unless they're playing in a string ensemble that constantly performs unseen sheet music. In that context, there’s a massive amount of information to decode all at once: key and time signatures, modulations, bow directions, and dynamics. Not to mention the harmonic knowledge required—since you might need to skip notes on occasion, knowing the harmony ensures you can instantly recognise and target the essential tones.

I think that's exactly why reading two bars ahead is necessary for complex pieces: you need the buffer time to gather all that information. But with simple fiddle tunes, there's really not much to decipher. There are no bow directions to follow (you just make up your own), no dynamics, hardly any shifting, and simple structures with plenty of repeated phrases. It's really just the dots and the rhythm.

Personally, I'm not sure how many notes ahead I'm reading, but it must be at least a few since I can recognise the tune as I go. For me, it all depends on note groupings—usually about four notes per group. If these four-note scale fragments are recognisable, I can play them without looking at each individual note, which puts me about two beats ahead. And if there are many recognisable groups bunched together or If the notes form clear chord tones, I could be much further ahead. I think it just varies depending on the phrase.

I’m pretty sure I just read what I’m playing. If anything gets complicated I just work through it to learn it and memorize it. In a performance situation I just use the manuscript as a rolling reference.

Sometimes the sheet is in full focus with the conductor in my peripheral vision and sometimes the conductor is in focus and the sheet rendered to the peripheral. Maybe I can glance ahead when it is all learnt. 

For the past two weeks I've been using sight reading to get my fingers into "The Last Shot Got Him".. Now that I have the fingers working I'm listening to a recording to get the 'feel/phrasing' of the tune. There is at time/place for sight reading but I can't imagine anyone actually Sounding good on this tune while only having sheet music..I'm keeping one eye on the sheet while listening and eventually two things will happen. One, I'll no longer need the sheet music and two, I'll start getting creative with the great tune....