Keymap for positioning objects :

Ctrl + Scroll : Increase or decrease the horizontal count of objects

Shift + Scroll : Increase or decrease the vertical count of objects

Ctrl + Alt + Scroll : Increase or decrease the horizontal spacing

Shift + Alt + Scroll : Increase or decrease the vertical spacing

C : Switch to circle positioning 

L : Switch to line positioning

Alt + Scroll : Control the rotation or scale mode

R : Switch to rotation mode 

S : Switch to scale mode