Looking for a EUC custom model for GraphHopper

Question

I am trying to setup a "good" EUC custom model for EUC (electric unicycle). Here is my first try:

{
  "priority": [
    {
      "if": "road_class == PRIMARY",
      "multiply_by": 0.5
    },
    {
      "if": "road_class == SECONDARY || road_class == RESIDENTIAL",
      "multiply_by": 0.7
    },
    {
      "if": "road_class == TERTIARY || road_class == UNCLASSIFIED",
      "multiply_by": 0.8
    },
    {
      "if": "road_class == CYCLEWAY",
      "multiply_by": 1.0
    },
    {
      "if": "road_class == MOTORWAY || road_class == TRUNK",
      "multiply_by": 0.0
    },
    {
      "if": "max_speed > 80",
      "multiply_by": 0.2
    },
    {
      "if": "surface == ASPHALT || surface == CONCRETE",
      "multiply_by": 1.0
    },
    {
      "if": "surface == GRAVEL || track_type == GRADE3 || smoothness == INTERMEDIATE",
      "multiply_by": 0.6
    },
    {
      "if": "surface == DIRT || track_type == GRADE4 || smoothness == BAD",
      "multiply_by": 0.3
    },
    {
      "if": "track_type == GRADE5 || smoothness == VERY_BAD",
      "multiply_by": 0.1
    },
    {
      "if": "max_slope > 0.2 && (surface == GRAVEL || surface == DIRT || smoothness == BAD) || smoothness == VERY_BAD",
      "multiply_by": 0.2
    },
    {
      "if": "road_class == STEPS",
      "multiply_by": 0.0
    }
  ],
  "speed": [
    {
      "if": "true",
      "limit_to": "20"
    },
    {
      "if": "surface == ASPHALT || surface == CONCRETE",
      "limit_to": "25"
    },
    {
      "if": "surface == GRAVEL || track_type == GRADE3",
      "limit_to": "18"
    },
    {
      "if": "surface == DIRT || track_type == GRADE4",
      "limit_to": "10"
    },
    {
      "if": "track_type == GRADE5 || smoothness == VERY_BAD",
      "limit_to": "6"
    }
  ]
}

Result is not satisfying. It makes too much detour:

It should find this:

I don't see any reasons from my criteria (road_class, slope) why it does this detour. Any idea please?

EDIT: the max_speed constraint is the cause. If I put 0.4 instead of 0.2, I get:

Does someone has managed to build a good one?