Wait, why blame the grain when the board was warped to begin with? That's kind of like blaming your saw for a bad cut when the wood was already bowed before you even touched it. A warped board is gonna fight you no matter which way the grain runs, and honestly flipping it around to "go with the grain" can just make the blade follow the curve and give you an even worse edge. Check flatness with a straightedge first, then worry about grain, otherwise you're just chasing the wrong problem for 3 hours.