I can't say I have ever seen an orderly boarding process for a Delta flight. Indeed, with nowhere to specifically stand, some 30% of the pax will loosely cluster in the gate area, often blocking the concourse. Most of them probably aren't in F but it seems rude to try to push your way through before boarding is called. So instead, one arrives at the gate and simply adds to the mess for a minute or two before the (inevitably slightly late) start of boarding.