Helphelp in finding target angle

guys please help me out its been 4 days working on this thing but cant figure out

suppose i am getting target head bone coordinates x,y,z
so i can find angle for which i can target on his head using simple trigonometry but whats the other point from where we have to calculate angle like if i use my position m_vecOrigin = 0x134; then it aim to head but when bot crouch my aim change to his head but when i crouch it dont change couz when he crouch his head position z coordinate changes and my calculation works but when i crouch my z coordinate dont change couz i use m_vecOrigin = 0x134; offset...
so please help me what i use or suggest me something

Use the bone matrix to get the head bone location of the enemy. This however is something I don't know how to do. So yeah instead of using vecOrigin which you should just use to find the players head location, use the bone matrix.