I do mostly light roast espresso and I have battled underextracted espresso. I struggled more when I used a Mazzer. Now I use an EK43 and do 18g dose to 45g yield mostly and can only do 18g to 36g if the roast is a little darker. Yes, make sure temp is up, grind is fine, distribution right, use VST baskets and experiment with dropping the dose a little and if needed more yield from the dose. The reward is a very fruity and sweet espresso without those roast flavors (I don't enjoy those).