Evolution in cat size tends to be governed by niche partitioning: cat species don't thrive when in direct competition with other carnivores of similar size.
In much of southern Amazonia there are six 'common' cat species. In size order: jaguar, puma, ocelot, jaguarundi, margay and oncilla. They each avoid direct competition by feeding on different prey appropriate to their size.
However, the jaguarundi and similar sized margay avoid competition by one being diurnal, the other nocturnal.
If they'd diverged in size instead, they'd encroach on niches already occupied by ocelot and oncilla.
So the whole cat guild can be viewed as coevolving in such a way so as not to step on each other's toes.