A wire that is for flat and horz only, will be fluid enough to flatten out and a wire that is for any position may freeze too fast to really flatten out with out working the puddle. Work the arc to the leading edge of the puddle and melt the base metal and then back to the middle of the puddle and fill in where you have melted the base metal as you travel forward. This motion helps flatten out fillet welds. It will give you a rippled affect like it was done with stick.
"Most" FCAW wire that comes from the factory with those machines is E71T-X wire and is for any position. The "1" is the indicator that lets you know that it is an any position wire. If the wire is E70T-X, the "0" would be an indicator that it is for flat and horz. only positions.
An increase in travel speed and more heat will help with the "piling" up, along with proper preheat of the material. The materials you are working with don't need much heat, if any, due to the thickness. Shielding gas mixture will play a part in freezing the molten puddle as well. The amount of CO2 in the mix determines how fast the puddle will freeze. CO2 is cold when released into the atmostphere after being compressed and helps cool the puddle to make it freeze quicker.
John Wright