Wan uses historical data combined with climate data with some,seasonal adjustment sprinkled on top to lower the barrier of entry for flex like behavior. you can think of it as a predictive model with reactive qualities.
Flex, is fully reactive and thus requires precise configuration of the advanced zone attributes.
With wan you select the amount of time you want to water as the main driver, with flex you can make subtle adjustments to duration but it's run time is a derivitive of pr, root zone, soil type, crop coefficient and zone efficiency. You then use the managed allowed deplition to control the interval of the schedule.
I ran wan for a week and dropped it so I'm not the best to advise for subtle wan adjustments, but I'm getting there...I have a shadow schedule with 4 zones that are not hooked up to observe its behavior but it is starting to get in the way...so I might drop it. And I like an idiot gave away my older unit to spread the crack around the hood.
In short and I mean no disrespect, it sounds to me like your advanced zone settings are not align with reality. Most commonly the pr and or root zone is wrong.
I'll take the Pepsi challenge with wan/flex, if you have seen the documentary pumping iron, wan is like Lou ferigno and flex is like Arnold Schwarzenegger but I'm totally biased here...and remember, Lou became the hulk and Arnold killed the predator so who knows in the end.
We can explore your config if you like...but post that in the flex topic.