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i understand your base circle point of view, but what about the additional lift?"

Additional lift has nothing to do with valve clearance. What you're doing is ensuring the gap when there is no load on the valve spring is correct. Once there is load on the spring by the cam lobe, clearance is 0. Again, you're only adjusting the gap at 0 lift to ensure you're getting the maximum effect from the cam lobe...

Valve clearances "must" be adjusted without silencers for the very reason you just stated. The silencers are rubber and will harden after a few thousand miles. Setting valve clearances with them in defeats their purpose. They are designed to take up the extra few thousandths and keep the lifters in contact with the cam and thus keep the valve train quiet while yet retaining correct clearances.

Dale