To give yourself the best chance of a avoiding the obvious running downwards try and get it on a turner or by hand if its done manually, also warm the etex first by putting the bottles in hot water..not boiling though! leave for at least 30 mins this will thin the etex and create less bubbles, mix thoroughly and leave in a warm place for a while, this will depend on where you are because humidity affects the way etex behaves, 70-80 degrees is a good temp range.
Check after 10-15 mins and it should now be starting to thicken, if not leave another 10 or so, then apply, it should have less chance of running if its thicker obviously, then keep an eye on it and turn every 5 mins if done manually, it should be ok to leave after a few hours if left in warm conditions of about 80 degrees.