tracking an empty to follow an animated Extrude along a curve

By manipulating the ‘bevel factor’ of a curve i can get the curve to extrude along itself. which works great.
What i now need is an object that matches the velocity of the extrusion.

i have managed to get an empty to do this by adding a ‘follow path constraint’ this also works great. i set the number of frames for the follow path to match the bevel factor.

however, they run at different speeds. even though they finish at the same time, the ‘bevel factor’ & ‘Empty’ run completely differently, thus the empty is sometimes at the end of the extrusion and sometimes way behind. even though they both have the same start and stop time.

I can adjust manually and keyframe with the ‘Evaluation time.’ however this is not an option as i have a very, very complex imported SVG from illustrator and hand animating these values would take the rest of my life…

The reason i want the empty to follow at the end is so i can attach effects, export as a null for after effects, and set the depth of field of the camera to stay with the object.

anyway, i really need some advice/ideas for this to work.

I tried to see if there was a pattern in the difference that maybe a math boy could compensate with some kind of expression, however im no where near clever enough to find any pattern in the values.

i believe the difference may come from the fact that the end bevel factor is from 0-1 while the eval time is from 0-100. this however is just a guess.

i will post some screenshots if requested.

thanks for any advice.