Just in case photos (to be added) disappear in the future.
OK, 1989 NA mpfi EA82 slugs below

here is a description of a piston found in an mpfi EA82 NA 1989 casting date on block
imagine a flat top piston, now see arrows indicating towards front of engine block, and other markings indicating R or L, R are fitted to block same side as a driver sits in RHD worlds.
Next pic, below is from hmmm, EA82 Turbo mpfi, piston tops a few thou above the deck, and according to the previous, previous owner was a strong EA82T until it blew a hose - Fury Leyland Vortex, with a single wire knock sensor in it

You still got image of flat tops in head ? Well there is a recess in piston top, it is not equal as it is deeper on the lower side of what look like a pair of cuircular depressions for valve clearance, ramping up to the flat top of the piston.
Word is if you use EA82 NA mpfi pistons you get higher compression

What I have trouble conceptualising is if we have three different piston designs - how are all of them same cc's ?
EA82 mpfi TURBO pistons, running 7.7:1 comp ratio in 85.86 models have flat top with an even depth recess in the centre