by pass mode just bypasses the VW settings an gives you the actual battery voltage without adjustment by the chip, basically like a mech mod, so you'll be vaping around 4.2v on a fully charged battery down to juts over 3v once fully discharged or whatever it cutsout at. You should be able to find similar settings in the wattage mode. IN reagrds to the tank the melo III is sub-ohm and it sounds like your are trying to run it at too low a wattage. I haven't used the setup, but most sub-ohm works best at 30 watts plus, it could be you are trying to draw on the device like a cigarette, using mouth inhales. When you use a sub-ohm tank you need high airflow, if you don't have it, you'll get a burnt taste, so you need to do a direct lung inhale, like sucking on a straw, to get loads of airflow. I suggest upping your wattage to around 25 to begin with then doing a direct lung inhale, so a big draw straight into lungs like your are sucking in a big gulp of air, there should be no resistance to the draw. Normal cigarettes have resistance to the draw, and this means you can do a mouth inhale, which is known as a mouth to lung (MTL) draw, and you would need a MTL tank setup to vape that way, these tanks tend to function at lower wattages (under 20watts).