The maxHeight property (number) specifies the maximum modal dialog height in pixels when DayPilot.Modal.autoStretch is enabled.
DayPilot.Modal.maxHeightnullIf not set, the dialog stretches until the free space below it is equal to DayPilot.Modal.top.
const modal = new DayPilot.Modal({
autoStretch: true,
maxHeight: 600,
top: 20,
// ...
});
modal.showUrl("/dialog.html");