Mauritius, page-8

From memory, the ill fated Reunion Island site was only 600 metres from the shore. That would support your theory that there is a steep drop off from these volcanically formed islands. RI is not very far from Mauritius so likely to have similar geology.

I recall from my navy days that Nauru is the tip of a pinnacle thrust up from the sea floor by volcanic action. I remember sailing quite close (about a kilometre) to it in the aircraft carrier I was on, in deep blue water.

https://en.m.wikipedia.org/wiki/Geology_of_Nauru

A drop off of 4300 metres, imagine that? I guess that rules out Nauru for point absorbing wave energy devices.