Leaf spring shackle question

[rohrt]

Never really gave it much thought but replaced the stock rubber bushing with poly and re used the stock end link shackle setup. Its a bit hard to see but the end links are a bit bowl shaped more for a rounded end rubber bushing (see 2nd pic).

You guys see this as a problem? Would a flat end link be better?

How tight should the shackles be? Should it still be able to move by hand? Should it just be tight enough to take up the slack and still move without pinching it to the point of no movement?