chevvron,
I think the link connects to a page with more or less just basic info, an overview of aircraft data and performance, mainly used in the intital ATM training.
If I'm not wrong, IFPS is using a highly realistic BADA profiles/specifics. (
https://www.eurocontrol.int/sites/de...w-bada-apm.pdf and
https://simulations.eurocontrol.int/...ormance-model/). These are mathematically developed profile envelopes, for all stages of flight and a number of acft types. Of course, they are based on more-or-less average style of flying, and do not take in to account the possibility of "insane" or military-jet style flying - even if modern business jets are capable of doing it safely... The models will probably work in more than 95% of processed FPLs - they're just not perfect.
I am not an expert, so if there's anybody more proficient in this, I happily accept corrections.