You want a little delay before it triggers otherwise it'll be constantly triggering when rocking the wah and hitting the stop. Whether using 5% or 95% for the off value when auto engaging, if it triggered instantly it'd be a very obvious and unpleasant change in the sound.
Using the Paragon, when set to "Fast Pos" the delay seems to be somewhere between 0.65…1 second on my FM3, based on using a stopwatch and testing multiple times, but the times appear consistent for other wah types as I doubt that the speed is type-specific. I don't find <1 second an objectionably long time as I use the slow (~3 seconds) or medium (~2 seconds) position setting to avoid those false "off" bypasses.
See
Alternative to Auto-Engage for an… uh… alternative to auto-engage.