https://perfectdailygrind.com/2018/04/how-to-control-brew-ratio-for-better-espresso/

Fast extractions (15 to 20 seconds) result in acidity, reduced sweetness, and high bodies.
“Standard” extractions (21 to 35 seconds) tend to be sweet, acidic, and well-bodied.
Slower extractions (36 to 40 seconds) can be bitter and low-bodied.


IS THERE AN IDEAL BREW RATIO?
The “best” brew ratio will depend on a lot of factors. Many people would consider 1:2/50% a standard espresso. However, as third wave coffee culture has evolved, you’ll find a wide range of brew ratios in use to suit people’s tastes. What’s more, since every coffee is different, the best ratio will vary according to the origin, roast profile, and more.

To master brew ratio and create the best recipes, you will need to experiment. Start out with a 1:2 or 50% ratio and then slowly begin adjusting it. Make sure to keep everything else constant for the most useful comparisons. Pay attention to extraction time, taste the espresso, and take notes.

Over time, you’ll develop an understanding of the complexities of brew ratio and how to play with it to match both the beans and the desired cup profile.