i have rifles with the touch holes in just about every position of a clock. they all are very reliable with good dry prime and good flint.
for years i was hung up on the sunset position but time has changed my thinking.
that said, when i am drilling a touch hole or installing a liner, just for continuity i place the hole at the sunset position. this usually puts it centered on a flat.
just my 2 cents.
i have acquired several very nice barrels cheap because of this. a builder gets the barrel and freaks out on the vent placement. so i guess i should help perpetuate this preception!