The 1+1/4 squat can be used as either back squat or front squat. It places more emphasis on the bottom position in a squat.
Set up in either the back squat or front squat and perform the eccentric portion of the lift as per normal. At the bottom of the lift drive up to parallel under control, pause, return to the bottom of the lift and then drive up to full extension. Do not relax into the bottom and ensure tension is maintained through the legs.
I like the 1+1/4 squat to help strengthen the upright position when driving out of the hole. It places more emphasis onto the VMO and glutes due to the double drive out of the bottom.
The purpose of this exercise is to strengthen the bottom position of the squat and the activation and strength of the VMO and glutes. Therefore, the weight shouldn’t be so much so that these positions are compromised. Go heavy but with good form. If the positions cannot be maintained then the exercise is null and void. I have found this exercise to be most beneficial in the 3-6 rep range with a controlled eccentric.