Replacement loo issue

The house refurb continues - to the downstairs cloakroom loo!
The existing soil pipe comes up through the concrete floor, with a 90 degree pan connector straight into it. Distance from soil pipe to wall is about 45mm. The pan connector is so far onto the spigot that its right up to the back of the pedestal on the old loo
I've just checked the dimensions of the loo I replaced upstairs a while ago (a Roca) and pedestal is a good half an inch further back towards the wall than the old loo so won't be suitable without some fettling to bring the new loo further out from the wall (e.g. putting a couple of lumps of timber between wall and new cistern, or an extra layer of plasterboard on the entire wall). I assume this is all due to modern loos having smaller cisterns and being more compact.
But before I do any of this, I just wondered if there tends to be any variation between manufacturers and/or anyone who gives decent diagrams for their products with full dimensions.
TIA, Midge.
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