HiCS:GO uses the well known Source formula for calculating sensitivity. Check a few things in the config file that can affect the sensitivity, they should be the default values here:
m_customaccel ""0""
m_forward ""1""
m_mouseaccel1 ""0""
m_mouseaccel2 ""0""
m_mousespeed ""1""
m_pitch ""0.022""
m_rawinput ""1""
m_side ""0.8""
m_yaw ""0.022""
Escpecially m_yaw is important. I just fired up CS:GO here, and used your numbers (2.6 sens, 400 DPI and 106 FOV), and the calculations are spot on. Your measurements are so far off, something must be wrong somewhere indeed. Fist of all check the settings I listed here, also if you can try in another Source based game, or any other game for that matter, and see if they also are off.Regarding pixelskipping, you are just below with your settings