The balance component of the Air Squat can be overlooked: weight evenly distributed across both feet, with big toe, pinky toe & heel planted on the ground. A strong base effectively exerts force through the ground to the top of the squat. It is only “air” ( body weight), but force is still required, so be efficient with it!
The top of your pushup should be exactly the same as your plank — hips tucked & core engaged. This remains the same during descent and back up too. Holding this position uses UB Pushing muscles without compensating or “worming” off the ground.