I'm fairly certain that you aren't accounting for uncertainty properly, especially with long-tail events. Let's say you have a ticket to enable a config flag. That's low risk and relatively small. There's still a risk that there's the flag hits a silicon bug. Does your estimate reflect that risk and is it useful if 95% of tasks don't hit those issues? Consider also that estimates delivered by contractors or even other teammates will not reflect these risks and thus you look correspondingly pessimistic or even lazy.

For context, my team is in exactly this situation with several silicon bugs we found last month.