You are centering all your flakes on a spline. I think you might have better luck by extruding your text and placing the flakes on the surface. Then using the dynamics to avoid collision. (extrude distance of 0 so its still flat.)
Also using the random effecter to get more size variation will help you fill in the desired area.
If you are set on the spline effecter try setting the spline interpolation to “uniform” this will spread your clones out evenly so they don’t bunch up in the corners. Also by using the random effecter you can add some Z depth and removing collision.
Hope it helps.
/Randy