I don't think your point on size is correct actually. Belgium is the same size as Portugal and their slope of decline has been one of the fastest in Europe. You mention some other small countries and previously Luxembourg but also Malta had very steep decreases in the first wave too.

The bottom line is that Portugal has taken far less radical restrictive measures than some of the other countries where you see bigger decrease, which is why they announced a toughening of some of them in the past 48 hours.

I think another fair point is that in fact, countries which show a steeper increase tend to see a steeper decrease, whilst those where the increase was very progressive has a decrease which tends to be slower as well, and that's likely a mechanical effect of them having actually had some sort of restriction before (slowing down the increase then, but also meaning that new measures are only incremental later and thus are not as massively different in terms of contact as the prior situation).

In terms of sheer size, however, I'd say that if anything, it is exactly the oppositve of what you say and that on balance, the larger the country, the lower the scope for fast decrease.