how deep for rack lockouts

[rjl296]

i go about 6" down for my tricep exercise- is this right ?

 

[JDarty6173]

I rotate 2 different heights.. One is about a 7-8 inch lockout and the other is about 3-4 Inches. The 3"-4" i feel nothing but triceps but on the 7"-8" my delts to get involved some....