As long as you have a 100% working torque tool, and you know how to apply it, then follow manufacturer's recommendation.
I have seen friends using a torque tool as if it was a cheater pipe, extremely scary.
The difference between 20 and 28 is a tab more, so it is not that much. That is why is better to take some items to a lbs, then again I have also seen mechanics who rarely use a torque tool and are excellent mechanics.
Is better to be safe than sorry.