Do I have to really use Substance Painter for an upper back tattoo?
In short, yes. There is no way to do it precisely in CC even parting it (not to mention spanning across UVs - body/head/arms).
https://forum.reallusion.com/FindPost482713.aspx
Ironically, even RL own back tattoo example featuring 2 range maps created in 3-rd party app such as SP or 3DCoat.