('Stands up ready to have bricks thrown at himself')
When I last spoke to a piston manufacturer many yeras ago about this subject, great surprise was the result, how so??
The manufacturer retorted that "As we are the only people that know the actual percentages of the components for the piston alloy and its manufacturing process, we are the only people that know what size to machine the piston to for the correct required running clearances, providing the boring machinist does the job to the actual bore size".
What this means is that 'standard bore' is exactly that - not + or - 'the machinist's guesstimation factor', in the same way as +20 on standard bore is also exactly that.
That's why competition pistons are made with the required clearances and road pistons for the same engine are different and forged pistons are a different size to cast pistons for the same engine.
problem occurs when you are using road pistons for competition use....or different fuel.
My goto Engineer (of almost 40 years) has followed this mantra for years and does not suffer consequent problems when correct 'running in' requirements are observed.
(Waits for bricks to arrive!!)