Clearly, no one is going to hit 500+ HRs and spend the bulk of his career batting in the back half of the batting order.
And as the leader lists for batting order positions (BOP) #5 and #6 will demonstrate, many of the leaders on these lists didn't actually hit the most HRs while batting in these lineup slots.

Norm Cash, #2 on the BOP #5 list, actually did hit more homers in that slot than anywhere else. Cash batted fifth in 156 games dhring 1961, the year he hit .361.
Next: Ernie Banks. Mr. Cub hit 195 homers in the cleanup slot, as opposed to 161 in BOP #5.
#4 on the BOP #5 list is Robin Ventura. His 159 HRs is the first instance of a batter hitting more than half of his lifetime HRs in the #5 slot.
Orlando Cepeda, #5: once again, more HRs batting cleanup (187) than batting #5 (159).
So...four of the top five HR hitters in BOP #5 are what we might call "carpetbaggers."
Now, how about the #6 slot? Will that "carpetbagging" pattern hold?
Right out the box, Graig Nettles grabs our thesis by the neck and throws to the floor for a takedown. Graig hit more homers batting in the #6 BOP than anywhere else, though his overall percentage of HRs hit while batting sixth is only 37% of his lifetime total.

Our #3 man on the BOP #6 list, Vinny Castilla, also shows his highest HR total in the #6 slot, but once again his percentage (35%) is low.
It seems that these are guys who found themselves moved around in the batting order a good bit more than hitters in the key lineup slots.
Jay Buhner had a neck-and-neck race between #5 and #6, with #6 having a razor-thin edge when all the precincts were counted (110 to 105).
The #5 man on the BOP #6 list, Gil Hodges, actually did hit more homers in the #5 slot (138) than in the #6 slot (110). He also had 400+ more plate appearances. When we look at Hodges' BOP splits by year, we see that Walt Alston moved him around a lot, from #4 to #7. Alston did a lot more lineup tinkering with a group of hitters who you'd think might just be set down into a fixed batting order and allowed to let it rip; someone might have fun looking at that in greater detail.
There are a lot of catchers on this list: Posada (#2), Gene Tenace (#6), Carlton Fisk (#7, though the original Pudge hit a few more HRs batting fifth than sixth, thanks nearly a thousand more plate appearances), Javy Lopez (#8), Benito Santiago (#12!!), Ed Bailey (#14), and the other Pudge, Ivan Rodriguez (#25, though oddly enough he hit more HRs in the #2 slot than anywhere else).

Hitters common to both leader lists: Gil Hodges (#8 on BOP #5 #5 on BOP #6); Ron Cey (#11 on BOP #5, #16 on BOP #6); Lee May (#12 on BOP #5, #21 on BOP #6); Gary Gaetti (#18 on BOP #5, #11 on BOP #6)
Most homers in a single season for BOP #5? We already told you, but just so you won't strain your neck: Jimmie Foxx, 58, 1932. And BOP #6? Troy Glaus, 39, 2000. The top five single-season guys for BOP #6 are, perhaps unsurprisingly, clustered between 1996-2000; there's a much wider time range for BOP #5, from Foxx in 1932 to Chris Davis (#4 with 38 in 2013).
We'll be back with the dregs (#7-8-9) next time. Stay tuned...