Why Do Shield Cents Show Doubling On The Devices So Often?

Couldn't fit a more descriptive title under the character limit, but my actual question is why do shield cents so often show doubling on the devices when nearly all doubled dies on single squeeze coins show at the center of the design (e.g. Homestead window/pump, Minnesota tree, nickel doorways, LMC column doubling)? Also, why do nearly all the examples of this doubling on the devices occur on Philly minted coins, while Denver coins typically show more standard doubling on the earlobe? Is there something different about the way Philly is minting these coins to the way Denver is? Is there a reason why shield cents show more doubling on the devices than other denominations?