If when you turn the bars it moves the slides you either don't have long enough cables or they are badly routed, at no time should this happen and I think it would be an MOT failure in the UK.
You certainly shouldn't need 1/8" slack in the inner to compensate for this, you are just masking the problem.
You certainly shouldn't need 1/8" slack in the inner to compensate for this, you are just masking the problem.