"Swept trace: HitPosition is the surface, EndPosition is the shape centre"

A decal or impact effect placed at trace.EndPosition after a .Radius(r) sphere-cast floats a full radius above the surface instead of sitting on it.

For a swept sphere/hull trace, the result carries two positions:

• HitPosition — the true surface contact point (result.HitPos)
• EndPosition — the swept shape's centre at impact (result.EndPos), offset from the surface by the radius

A zero-radius ray trace makes them coincide. But a .Radius(r) sphere-cast puts EndPosition a full radius above the surface. StartPosition is returned when nothing is hit.

Use HitPosition (and Normal for the surface normal at the contact point) for any surface effect:

var tr = Scene.Trace.Ray(origin, target)
    .Radius(16f)
    .Run();

if (tr.Hit)
{
    // Correct — sits ON the surface
    PlaceDecal(tr.HitPosition, tr.Normal);

    // Wrong — floats 16 units above the surface
    // PlaceDecal(tr.EndPosition, tr.Normal);
}

HitPosition is the actual contact between the swept shape's surface and the world geometry. EndPosition is where the shape's origin (centre) would be if it stopped at that contact — useful for repositioning the swept object, but wrong for surface effects. For a ray (radius 0), the shape's centre IS the surface contact, so they coincide.