I had to go adjust my monthly down a bunch based on my own usage data, and the website is like "OMG YOU'RE GONNA BE IN SO MUCH DEBT IF YOU PAY THAT LITTLE" with this crazy graph of account balance going off the bottom of the scale.
I then look back at my own graph (from their own data) and it's like "yeah you're actually still overpaying by a bit".
keep in mind that this is all smart metered. they have hourly data from my meter to measure how much I've used, with historical data going back years. but because they based the model on typical usage it completely breaks when faced with near-constant energy consumption throughout the year, thus doing the opposite of what the model was supposed to do.