I don't really know how the control input maps to delay time either. What I would do would be to take the 0 - 0.5 triangle output as you have and then run that into a scale/offset block. You want the range 0 - 0.5 to map to -0.25, 0.25 (SOF 1.0, -0.25). Run that through the multiply. Then you want to add this to the offset, say, from a pot. Use a 2:1 control mixer block to do the addition. The offset would have to start at 0.25 so we don't send negative values into the servo delay's time input when the width is up full. So from the pot, run it through a scale/offset mapping (0,1) to (0.25, 0.75). That also leaves 0.25 on the top end. Quite likely you will have to adjust all of this (and the servo gain) interactively.
This at least gets you to where you can set a fixed offset and then have the triangle scaled by the width control wobble around it.
Does that help?
DL