Do you only let your espresso shot run the standard brew ratio 1:2 ? So if you put in 18 grams of coffee, you stop the shot after 36 grams in the cup ?
This fits dark roasted coffee well. But lighter roasts might very well have nice flavors beyond the 1:2 brew ratio.
Search your coffee by tasting drops during the espresso shot
Let an espresso shot run really long while you taste with a spoon to follow what taste is extracted along the way. Provided that you got a suited grind size and don’t have channeling – the development in the taste is:
Very sour and sharp at first
Then sweet and nice aroma
Then bitter
Then thin
With a dark roast this is released fairly quickly: with around double the amount water than coffee – the 1:2 brewratio.
But light roasts are denser and got less solubles than dark roasts. So the taste is released slower. This is why longer preinfusion makes sense. But also running a longer shot, like 1:3 or sometimes even 1:4
When I brew a light roast espresso, I always explore the coffee on hand by tasting while the shot is running.
Using 17 grams coffee in the portafilter, I skip the first 10-15 grams because they are always very acidic.
Then I taste. Catching just a drop with a teaspoon.
See my video https://www.youtube.com/watch?v=VCovMAG2LXM
Then I can follow the extraction. When it starts to fade or get bitter, I stop the shot.
The best way to know how what brew ratio suits a given coffee, is to taste during the shot.