Trying to do a stock hp tune with 200% overs would be very difficult, and I'm not sure why you would want to do that. If all you are wanting to do is limit max hp, then there are easier ways to do it then adjusting the duration table.
A couple of comments... Injector flow is not linear to injector duration. If you look at an injector flow sheet (especially easy to see if the flow sheet includes a graph), you will see that the amount of flow delivered changes dramatically with duration. If body mods have been done to the injector, then in most cases low duration fueling will also increase.
Depending on the year most ecm calibrations will cut any injection event that is less then 160us. So at an idle if you cut the duration to much, then the ecm may switch back and forth between a single event cycle and a multi event cycle. This will cause at the very least a rough idle, if not a "lope".
If you truly wanted to use the duration
map, to remap the injector output to match a stock injector delivery, you would need to determine what the injector flow is at every point in the
map. In other words for that particular injector how much flow is happening at the intersection of each x and y axis. I have never seen a flow sheet that gives you that much information, so you would end up having to plot the know points, and extrapolate from there.
Hope this helps...
Paul