Light roast espresso needs water at 199°F to 205°F (93°C to 96°C). Dark roast requires 188°F to 194°F (87°C to 90°C). That's up to a 17°F (9°C) difference between two bags both labeled "espresso."

Same machine. Same pressure. Entirely different needs.

If your machine has temperature adjustment and you're not using it by roast, you're leaving real flavor behind.

Are you brewing all your roasts at the same temperature?