Just how much smaller do you think an engine could be made by making the cylinder walls thinner?. A 1.6 is not actually a big engine in the grand scheme of things. I used to have a 1.6 Capri, it's engine looked tiny in an engine bay big enough for a 2.8 or 3.0 V6!. I seem to remember reading that the engine block of Fords 1.0 (ecoboost) can sit comfortably within the confines of a sheet of A4 paper. And that can produce up to 140bhp, though perhaps without a great deal of reliability!.

To some extent it depends on the way the engine range was designed.

All Ford x-flow engines shared the same cylinder spacing thus the 1.1 and the 1.6 had exactly the same footprint under the bonnet. However, the 1.6 was a tad taller. Still difficult to tell just by looking under the bonnet which engine it was.

Same with the original range of Zetec engines, 1.6 through 2 litres the blocks looked identical except for the engine size being cast into the metal. As with the x-flow a glance under the bonnet would tell you little. Eventually the 1.6 was replaced by the Zetec SE (the Yamaha derived engine still being used by Ford), the Zetec 1.6 was a huge hevy lump.

But the Rover k series was different. It was designed as a 1400 and was pretty compact. It was also available at launch as a 1.1. But as time went by a 1.6 and 1.8 was introduced and they are the engines that had most issues probably caused by stretching the engine beyond its design limits. Compared to a Zetec 1.8 the K series 1.8 is compact. I know several people who have reliable 2 litre K series engines in their cars but they have cost an absolute fortune to get into that state. I know of a couple who wish they had junked them and fitted a Ford Duratec.