odd bit of suck back.

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Wondering if anybody has a lot of experience or knowledge welding high pressure pipe.  I'm currently  welding 12 and 18 inch HIGH pressure steam pipe.  The first pass is tig, I do one more hot pass tig,  then I fill and cap stick.  Anyways,  the question I have is about the initial root pass.  I'm obsessed with looking inside the pipe to admire my penetration and to just make sure everything is going ok as every 3rd joint is xrayed.  The odd time I notice alittle bit of suck back.  Only on my top half though.  Never the bottom.  I've asked my foreman, and he said you're either going too slow, or your amps are too high.  Anybody else able to help me,  or explain what is going on,  it would be much appreciated since I am pretty green at this. Thanks Ps,  I'm posting from my blackberry, so its hard to proof read this.  Please excuse the endless sentences.  My cursor is messed up so there won't be any proof readin lol.
Reply:Well if its not what your foreman said then are you keeping your torch angle the same through out the weld.  The more you lay over your torch the more suck back can occur.  So if you under your pipe your torch could have less angle but as you go around to the top of the joint you could be laying the torch.
Reply:Now that I think about it, that's probably exactly it.  I'm probably pointing it too much on the top,  putting too much heat into it.  Thanks for the input and I will surely keep better attention to this and let you know how my next root goes.
Reply:i assume this suckback is occuring at your tiein at the top of the pipe? Iam also a welder at a coal fired power plant. Most of the stuff im working with is 8" to  2" sch 160, 1 1/4 chrome and 2 1/4 chrome. At the bottom of my pipe i start on top of my origional tack and go about as slow as i can to ensure i get enough penetration from 6:00 to roughly 7:00, and then its all easy from there, once i reach the top as soon as i come into my other tack i pour the heat to'r and lay the filler to it, once im half way into my tack i walk my puddle up the side of the bevel an extinguish the arc. I find guys tend to take their torch out too early and or dont add enough filler. Are you also doing a post heat treatment process ?