If you’re cutting out parts of the shot/brew, then you are inevitably getting a low extraction. I don’t say this as if it is necessarily a bad thing, especially if you are particularly after sweetness.
I don’t think this alternative route to a sweet spot is limited to espresso, nor levers.
You will have heard people say things like, “…aim for 19/20/21% extraction.” This is typical with normal/longer espresso ratios & brewed coffee, but there is a point much earlier on where the coffee’s character becomes apparent and you can get particularly sweet coffee (11-14%), with very low bitterness and less aggressive, off-putting acidity. This is already well established with very short espresso pulls like 1:1 to 1:1.3 and high dose, coarse grind, short steep Aeropress brews in particular.
This may be the region you are hitting on? Also discarding the first drops will lessen the impact of the bitter oily output you get at the very beggining.
I have for a long time felt that, if your espresso is typically bordering on sour/tart and you can’t easily shake it, that extracting even less can be the route to easier, more pleasant cups. If a little counter-intuitive in terms of shot speed/output.