for my Pico and mouth to lung I use the Melo 3 mini that came with it and use the 1.5 ohm Triton coils rather than the Melo ones , they have a much smaller airway and perform great , converts the Melo to a proper MTL tank BUT you can lways open up the air adjustment full for a cheeky lung hit when needed.
They also do a rebuildable coil which makes much much better use of the Melo3 mini that comes with Pico kits too its a fantastic short top fill tank modded a little and suits the stealthy Pico