Just to be clear-
The Fatboy is not an Ego clone, it is it's own device with similar dimensions as the Ego (Dubacco under D&B enterprises out of South Korea is the manufacturer)
The Fatboy operational voltages are as follows-
Full charge -Blue led 4.2v
Low battery warning- Red led 3.3v
Auto shut down-2.8v
Standard resistance 510 cartimizers are weak and flavorless under 5v, Boge LR carts or Kanger Horizontal is the only way to go when vaping carts on less than 5v.
Volt,E9,Bloog ect carts taste richer than 510 standard carts simply because of the differences in internal design making them run hotter, the Boge LR carts offer a a rich warm vape just as the 808 carts do, Kanger horizontals are reported to offer a rich warm vape on stock voltages as well (I have not tried the Kangers yet, vape mail on Thursday will correct that).
The cone shown in this image is a proprietary atomizer available only from the manufacturer.
To use your own cone on the Fatboy put a 510 to 510 Ego adapter on then add the desired cone, there will be a gap between the top of the battery and the bottom of the Ego adapter, this can be filled (for looks and gives the cone a threadstop) to fill the gap cut a section of vacuum hose or find a nut that fits or grab a small Lego tire, besides the added aesthetics the draw will become easier/better regulated.
That's a standard Ego cone that has been ground down slightly at the top to provide a wider opening (different heights are available to purchase though).