bezier curve on first and last points

[Anthonyk]

Hi !
I'm facing an issue with "open" splines. I'm trying to generate a perfect spiral, using bezier interpolation. The default distance for handles is calculated in order to get an almost perfect circle. 
It works great for all points except for the first and last ones when the spline is not closed. Is seems that the handle distance on those points have no effect on the spline.
Any idea for a workaround ?

Thanks for your support!
regards,
Anthony