Another tip to avoid possible chain suck is to think about tension on a chain and if you plan to take a lot of bumps and ride rough, you may want to keep more tension on the chain. So keep the chain in big rear, if you're on the small front, or better, middle front, big rear to yet more tension. The chain has some mass and inertia. If you jolt the bike, you might not feel like it's sharp impact because you're standing on the pedals with bent knees and can absorb it. But the chain is heavy metal and can get thrown unless tension keeps it on the gears. On MTBs with long-armed rear derailleurs, if you're in the small chainring up front and somewhere in the middle in the back, there's a lot of stretch left in that RD arm and it doesn't exert much tension on the chain.