MeiZhongTai, always challenging, had a good post on blockading Taiwan from the Taiwan perspective:

Susceptibility to Blockade
Taiwan’s two key ports (Kaohsiung and Keelung) are located on the west and north coasts, making them easy targets for a Chinese blockade. If it wasn’t clear enough, China pointed it out in 1996 by launching one missile each into the waters at the entrance to both ports.

The ROC Navy’s key bases also fall victim to unfortunate locations. Kaohsiung (including Tsoying, which is just north of Kaohsiung port) and Keelung are the ROCN’s largest bases. A blockade of Kaohsiung and Keelung would also be a blockade of both Taiwan’s largest bases. I am not familiar enough with the breaking of blockades to know whether having the ROCN inside the port being blockaded would be an advanatage or disadvantage. Is it either to break in or break out? My guess is that it would be better for the ROCN to be at sea when the PLAN takes its position. That would allow the ROCN more freedom of movement, whereas being trapped inside the port would make them sitting ducks to be disposed of at a time of the PLAN/PLANAF’s chosing.