French onion slow cooker roast

I am making this in a slow cooker for my husband’s family for Christmas Eve dinner. I seated on all sides to start and have been cooking on low for 6.5 hours, but it’s fairly tough still. I am running short on time and wonder if I can put on high for the next hour. The roast sticks up over the liquid. Could that be the issue? I’ve only made stews, etc that would cook the meat fully on the liquid.