As mentionned by Richard in this forum post https://discussions.unity.com/t/resolved-untiy-6-particle-trails-minimum-vertex-distance-has-no-effect-below-0-1-value/1491345, trail resolution is limited by frame rate. Only one point can be added per frame with particle trails and we have no plan to add built-in sub frame interpolation. Some API is available that can help implement this behavior (AddPosition)