how to make marker for tooltip bigger

Question

Here's my wandb vega. The problem is, right now, it is very hard to mouse over my line and get the tooltip to show. It is like you must hover over the exact pixel of the line with your mouse. How do I make the activation radius larger, so my tooltip shows up if I am approximately on top of the point of my line?

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "A plot for an arbitrary number of lines",
  "data": {
    "name": "wandb"
  },
  "transform": [
    {"filter": {"field": "${field:lineVal}", "valid": true}},
    {"filter": {"field": "${field:step}", "valid": true}}
    ],
  
  "title": "${string:title}",
  "layer": [
    {
      "selection": {
      "grid": {
          "type": "interval",
          "bind": "scales"
        }
      },
      "mark": {"type": "line", "strokeWidth": 5, "interpolate": "linear", "tooltip": true},
      "encoding": {
        "x":{
          "field": "${field:step}",
          "type": "quantitative",
          "title": "${string:xname}"
        },
        "y": {
          "field": "${field:lineVal}",
          "title": "y",
          "type": "quantitative"
        },
        "color": {
          "type": "nominal",
          "field": "${field:lineKey}"
        },
        "strokeDash": {
          "type": "nominal",
          "field": "name"
        }
      }
    }
  ]
}

Answer 1

You haven't provided the data along with your schema so it is difficult to answer your specific case. However, you should be able to adapt the example code from https://vega.github.io/vega-lite/examples/interactive_multi_line_pivot_tooltip.html to achieve what you want.