Calculate Route keeps ploting not the shortest route - here-api

Question

I'm using HERE's calculate route API to present routes on the map. In a few places, I keep getting results that led me here as I am seemingly unable to achieve reasonable results. Near Warsaw, my route keeps turning to the north towards the city just to turn south-west that is back in the main direction whereas there is a straight road that would allow achieving the same. My users expect routes to be as straight as possible and I am not able to defend nor explain such deviations as this in route plotting.
Request parameteres:
url: 'https://route.api.here.com/routing/7.2/calculateroute.json',
method: 'get',
params:
{ app_id: 'is-it-possible-to-learn-this-power-?',
app_code: 'not-from-a-jedi',
mode:
'fastest;truck;traffic:disabled;tollroad:0,motorway:0,boatFerry:0,tunnel:0,dirtRoad:0,park:0',
waypoint0: '54.11025,22.96542',
waypoint1: '49.19168,16.65446',
waypoint2: '49.59958,17.26838',
avoidSeasonalClosures: true,
language: 'pl-pl',
excludeCountries: 'CHE,DEU',
metricSystem: 'metric',
legAttributes: 'length,travelTime',
jsonAttributes: 9,
routeAttributes: 'shape,legs',
limitedWeight: 40 }
}
It is worth noting that at first I was convinced that I get this result because of the traffic settings, but it turn out no matter which option (concerning traffic) do I choose I always end up with what it look like the same route shape.
Result on map:
Result near the city:
My question is: is there a way to achieve a straight route without detours such as this in my example or maybe this is totally acceptable route but I am unaware of the reason?

Answer 1

A solution to this problem was to soft exlude motorways and to avoidSeasonalClosures as there are some near Warsaw and Wroclaw.
Now request params look like this:
{ app_id: 'i-am-the-senate',
app_code: 'not-yet',
mode: 'fastest;truck;motorway:-2',
waypoint0: '54.11025,22.96542',
waypoint1: '49.19168,16.65446',
waypoint2: '49.59958,17.26838',
avoidSeasonalClosures: true,
avoidAreas: '53.204942,23.05379;53.100605,23.254131',
excludeCountries: 'CHE,DEU',
legAttributes: 'length,travelTime',
jsonAttributes: 9,
routeAttributes: 'shape,legs',
limitedWeight: 40 }
The excluded area is the road near and north to the city of Bialystok as this road is not optimal.