I have an angled piece of chair-rail coming down the steps and meeting a horizontal piece that is running 90 degrees to it.
Naturally, the step piece angle will be much longer than the 90 degree and because it is 90 degrees back, the angle can not be divided in half as would be done if they were on the same wall...

What di I do??

Thankx...

Go horizontial before reaching the corner, usually at the nosing of the last step or the nosing of the next to last step.