1/4 lb is not big enough. 1/3lb or even 1/2lb works much better with the bun size so you can get decent burger thickness and have it reach the edge of the bun.

Add diced up raw bacon slices to the beef and mix in. And don't use salt, use Tony Chachere's creole seasoning, and plenty of it. Add Worchestershire sauce while you are mixing it up.

Flat top grills are fine, but flame grilled over charcoal adds additional flavor that you don't get from a flat top (or gas) grill.

And sprinkle a little more Tony's while on the grill and before you add the cheese.