Originally Posted by ThermionicScott

Chain angle can play a part. If you're already in the biggest cog when downshifting to the granny, it's more likely to overshoot the ring. Conversely, if you're still in the middle of the cassette, the chain angle helps encourage it to drop down onto the granny rather than going any further.

So while it's possible that your bike could be adjusted a little better, it would be good to get into the habit of shifting to the granny while you're still in the middle of the cassette and see a steep hill ahead. (Not while you're climbing the hill and about to stall out. )