Bag Machine Boost Slot

I’ve been playing this machine a ton the last few months and just posting what I’m noticing. We know on the 4th level up is the boost with the jewels. But I’ve noticed it takes a LOT of work to actually hit the boosted point. Obviously vulturing this slot is a great idea but is the optimal point when people have been contributing coins on level 3? Because I have never once seen it go quickly from the level before boost to boosted