A very underutilized work out ...well at my gym...i was wondering if i should do this workout in the beginning or the end of my leg workout

my leg workout looks like this now

dumbell lunges: 3x12 each leg

Squats: 12, 10 ,8, 8 , 6

Leg press : 12 , 10, 8 , 8 , 6

Leg ext. 3x 20 -15
super set with
quad curls 3x 15 -10

where would i add the sissy squat ..or i replace it with something?