Well, during the war the single bataillons were under different commands.
In peace the Fußart.Rgt.5 belonged to the V.AK (Posen).
By outbreak of war the regiment was divided in:
Staff - 5.Army
I.Btl. (schwere Feldhaubitze) - V.AK
II.Btl. (schwere Feldhaubitze) -XX.AK
For 1918 I have the following commands:
Staff - 2.Army
I.Btl. (1., 2., 3. battery) - 5.Army
II.Btl. (5., 6., 13. battery) - 26.Inf.Div.
III.Btl. (9. 10., 11. battery) - 5.Army
I´m still looking for further informations about the times between 1914 and 1918