What is the actual default walk speed for route planner?

Hi, I am using the https://api.resrobot.se/v2.1/trip endpoint trying to set a specific walk speed. I am using the destWalk and originWalk params and setting the relative walking time (in %) based of the default walk speed of 4.5 hm/h as specified in OpenApi documentation. It initially seemed to be working as wanted, however when I started testing I couldn't help to notice that the default walk speed doesn't appear to be 4.5 km/h as specified (which means my relative walking time values will not match the speed I want).

For example if you search form Arlanda Terminal 2-3 to Stockholm Nationalmusem: https://api.resrobot.se/v2.1/trip?format=json&lang=sv&originId=740020671&destId=740010947&date=2025-10-09&time=11:54&products=510&operators=!838&passlist=true&showPassingPoints=true&searchForArrival=false

one of the options says it takes 16 minutes to walk from Stockholm Centralstation to Stockholm Nationalmusem with a distance of 1348m. For a person to use 16 minutes to walk 1348 m they need to have a walk speed of 5 km/h (1,4m/s).

In addition, one of the other options says it will take 17 minutes to walk from Stockholm Cityterminalen to Stockholm Nationalmusem with a distance of 1565 m. That means a person has to have a walk speed of 5,5 km/h (1,53m/s).

(If any of my math is incorrect please let me know)

So why does the walk speed seem to vary and what it the actual default walk speed for destWalk and originWalk?