1.6 rockers achieve that ratio by altering the distance from the rocker arm shaft centerline to the pushrod cup centerline. On a 1.6 rocker the pushrod cup is moved closer to the rocker shaft or fulcrum. This is how you get a higher lift at the tip with the same lift at the pushrod. That means that if the pushrod was centered in the hole with a 1.5 ratio rocker, then there will be less clearance on the fulcrum side of the hole with the 1.6. This applies to ALL rockers and the only difference would be if there is variation in the distance from the rocker tip to the fulcrum. The head being used isn't mentioned but most heads were designed for a 1.5 ratio stamped rocker and even later aftermarket heads keep generally the same specs for the pushrod holes. It isn't necessarily a problem of the rocker design, but the system it is going into. You change something from OEM, you shouldn't be surprised if something else needs to change to accommodate it.