There are a lot of different things that could be suggested here, but with the gas and wire you are using I think the simplest one that requires the least amount of disruption to production for you will be to check your electrode angle, slow down(just a little) and put some left to right movement into it. Your angle should be such that the puddle is being held up by the arc, move a little left and then right. Basically just adding a weave to your downhand welding. I have seen some production welders point the electrode downhill and push the weld down. This is will cause exactly what you describe. I hope this helps.
Respectfully,
Mike Sherman
Shermans Welding
I wanted to actually try this before I responded so there has been a little delay. For the record- 28 volts about 200 in/min .045 wire 100% CO2. The gas may make a difference since it puts me in dip transfer where you may be in spray transfer. Wire pointing up at the puddle, motion into and out of the groove so you deposit metal on the bottom of the puddle for the depth of the groove. For me it wound up a little hollow on the front side but it didn't take long to put on another pass and some practice would probably make that unnecessary (I only tried it a couple of times). Clamped the filled one in the vice 1" from the weld beat it with a hammer to stress the back side- the plate bent. Clamped it close to the weld- it bent some then broke up the center of the weld. An acceptable result I believe. I hope this is of some use to you.
Bill