enlarging the holes around the bottom ring, making sure the center tube is clean and using a pair of tweezers to align and compress the coil and open up air channels around the coil may help but you are pretty limited with that design. an inexpensive
rta or a subtank may be a better option.I use 1.8 ohm
coils on my RTAs and get plenty of vapor and flavor. much more than my vivi- nova or ce4 which are similar designs to your halo.