Defending your candles

[Illuminated One]

For temples it's better to have them close to the borders that are in danger of getting enemy dominion.
For temples I think it works like this:
If the province with the temple doesn't get the dominion a random province next to the temple is the selected and checked for dominion increase. If the check fails a random neighbouring province is selected.
The same check is done again and if that fails another random province is selected and so forth.
That means the farther away your temples are from your borders the more checks have to fail and the possibility that the dominions goes in the wrong direction increases.

That said you might also want to look at the connections the province with the temple has. More connections outward than inward means a higher chance of of dominion going outward instead of inward.

[Illuminated One]

If you are preaching in a province with an enemy temple (either through stealthy preachers or a priest besieging a castle) do you get the bonus from the temple?