Agreed with drip. But to compute pr on drip is impossible. It is not a uniform system by definition and would need some intergalactic calculus to describe.
What I did was adjust the pr rate up or down until flex matched my existing watering time. It's hacky but I'm personally not investing too much time there, let's face it, if a plant or two needs more or less water, physical augmentation has to occur, not run time adjustments. I stuck with flex because because even on such a heterogenous zone I still got better performance with water usage with my annual beds and vegetable garden.
But I hear ya, drip zones with flex brings some butt hurt.
But flex is still the best thing for turf zones since sliced bread.