With a mech your mod puts 4.2v to the coil, well not really because of voltage drop but lets just say it does. So for example sake I am going to say you have built a .2ohm coil. This is just a quick little explanation you really need to do a lot of reading. Start with Baditudes blogs.
.2 ohm coil on that mech mod with 4.2v being pumped to it equates to around 88 watts. It also draws around 21 amps from the battery which is extremely important to know because it is VERY bad to use a 10amp CONTINUOUS rated batter for a build that draws 21amps. Do not pay any attention to PULSE ratings only CONTINUOUS.
If you use an atty with a 1 ohm coil, not POINT ONE but ONE ohm on a mech (4.2) you are only getting around 18w. It is not going to be a very cloudy vape. If you have a VW box you can force power to the coil. You are not only getting 4.2v and below. You can set it to 7v if your mod allows that and then you got a 1ohm coil with around 50watts of power behind it as opposed to 18w. IMO the coil area that is touching the wick logically plays a big part in the cloud output when you use regulated boxes. A nice twisted 26g dual coil with a net resistance of 1ohm set at 8w has 64w of power going to the coil which will produce an extremely respectable cloud, save battery life and most likely have better flavor. I do not understand why you would build low on a regulated box unless you had to in order to reach the max wattage out put due to a voltage cap or something. The regulated boxes I like to use have a 6v cap so I have to build a bit lower but if I had something with an 8 or 9v output I wouldn't even sub-ohm. I build right around 0.5 ohm on my Lemo II which sits atop my regulated box and I keep that box set at 5v so it produces 50 watts. If I had it on a mech it would do like 35 or something.
You have to use steam engine and play around so you see for yourself but I tried to give you a base understanding.