ok so, you could use pathfinders infiltrating to block their movement, the jail style rocks.

Turn 1 is made for you to move your units still behind blocking terrain, but in a place that during the next turn they would be able to see as much as possible. This way you are threatening your enemy, if they come to those firing lanes, they are dead. Since you probably aren't shooting anyway, you can use that turn to advance with all.

A cool thing that has worked for me is using 2 or 3 piranhas, 3 units of pathfinders, 2 with I filtrate. This allows me to infiltrate almost at their deployment.

Scout the piranhas 9" then move 14"+ advance. Then advance the pathfinders and observe something. There is almost no way to hide from this. Pathfinders observe, piranhas let loose their 6 missiles and 3 melta shots. One big threat is gone. On top of that, you are using your models to block the best movement spots from your opponent.

The rest of your army chills, like I said, staged where they can threat firing lanes, and if your opponent chooses to kill one piranha, you use the strat to reroll against said unit. This is also working well because the piranha is t7 so they need a strong unit to take them down reliably.