I don't think small nation is easier to control. For example, in Russia, whoever controls Moscow controls the country (don't want to explain here why exactly, so please just trust me in this). So, theoretically, a moderately big popular uprising against Putin in Moscow could gather 300K-500K protesters, and Moscow police would have just 30K riot troops to deal with it, plus 40K regular policemen. However, in a span of few hour, reinforcements from all over the country can be brought in from all over the country, bringing the number of riot police to 150K, quite comfortably enough to counter 500K protesters. And regional protesters have no real way to join the protests in the epicenter, because Russia is freaking big, travel is controlled by the government and can be ceased in case of emergency.
Side note: 2013-2014 protests in the Ukraine worked for a simple reason - not only protests enjoyed an overwhelming support in the capital, and had a fraction of parliament supporting it, Kiev is relatively close to western Ukraine, so many active protesters from there just got on buses and drove to join the fight and make the balance more even.
This said, I believe that the bigger the country, the easier it is to control, because government forces are way more mobile, which easier brings local numerical superiority. As for imprisonment, in a bigger country you just need more prisons, that can be achieved without much difficulties.
Side note: 2013-2014 protests in the Ukraine worked for a simple reason - not only protests enjoyed an overwhelming support in the capital, and had a fraction of parliament supporting it, Kiev is relatively close to western Ukraine, so many active protesters from there just got on buses and drove to join the fight and make the balance more even.
This said, I believe that the bigger the country, the easier it is to control, because government forces are way more mobile, which easier brings local numerical superiority. As for imprisonment, in a bigger country you just need more prisons, that can be achieved without much difficulties.