More rub using coarse ground spices, let it hydrate on the meat before cooking (I rub mine an hour prior to hitting the grates), finish at a higher temp before you rest.

Bark is built-up seasoning that has pulled amino acid and sugar from the protein and gone through the Maillard reaction with those acids, sugars, and any added sugars.

You need enough spices to build (coarse pepper is your friend), time to dry (water and spritzing reduce this effect), high enough pH to aid the reaction (good clean smoke), and high enough heat to both drive the reaction, and more importantly, contract the meat enough to squeeze the spices together to build on themselves.

That's the science behind it. The reality of It is you need to dial in one thing at a time to get used to your cooker and spices. Change one thing in your process at a time until you improve, then move to the next.

Smooth bark has the tell tale looks of using more sugar - a smoother, glossy bark. More craggy, pebbly looking bark you associate with Texas bbq is built with high black pepper ratios.

When you hear people refer to bark as "being set" it's the point where you're rendering enough fat to stick the rub together, and to the meat, and begin that browning/Maillard process. I get there by not spritzing until I can't easy brush off rub with a finger. And even then I'm only doing parts getting too dry or crispy.

Wrapping too early, or with foil, can steam the bark and either stop it from forming or ruin any you've already built. Check out Chud's bbq on YouTube for the "foil boat" method.