Akarnania

Modern Akarnania is part of the Aetolia-Akarnania nomos (nomos is the Greek name for region/district), which measures 5461 square kilometers. Akarnania is roughly between 1/4 (1365) and 1/3 (1820) of the entire nomos.

The boundary and river Acheloös has delivered plenty of fresh water and created the massive plains to grow wheats and grasses on that Homer mentions and the river still does.

... the glorious son of the King Nisos, son of Aretias, who led the suitors from Doulichion, rich with wheat and covered in grass.

Doulichion must be a region with great plains and a lot of fresh water to grow wheats and grasses, which Acarnania just happens to have: the Acheloös. The river supplies a lot of water and provides great plains. Islands usually don't have rivers like that.

Odyssey Book 16 line 378-380 Barry B Powell

The river Acheloös

So, Akarnania measures about 1600 square kilometers. One can read in the Odyssey:

The boundary between Akarnania and Aetolia is formed by the river Acheloös, 2 lakes and an area of wetlands. At the right hand, the river is presented by a blue line and the wetlands by a yellow one. With Akarnania to the west, along the Ionian Sea and Aetolia to the east.

So, Akarnania is rich of wheat and covered in grass,
Akarnania has a suitable size for the number of ships, Akarnania is close to the Echinean islands,
Akarnania is located east of Lefkada, our Ithaca,
Akarnania lies opposite Elis but,
Akarnania isn't an island.

Unless, of course, we assume the river is what makes Akarnania an island. Let's take a look in Akarnania.