If we look at the locations where Indonesia is said to place shore based anti ship missiles at, it should be clear that those locations are the chokepoints of the country's designated international sea lanes. As such, even mobile ground based coastal missile launchers won't have many options about where they can be deployed and redeployed after firing.
While the missile boats aren't invisible to radars and other detection methods, their small size and mobility is a big plus. Utilizing their shallow draft, they can sail close to the coast in attempt to make detection more difficult (i.e. using ground clutter as disguise). During attack, they won't have to sail too far from the shore since most of the straits / chokepoints are below 200-250 km wide.
Of course, this means that they should be assigned to both sides of the straits. Furthermore, there must be a dependable detection and targeting system as well as integrated combat management system for this tactic to be really effective.
In short, I'm picturing similar tactics with what Iran is planning to do to close the Hormuz strait by using many speedboats and fast attack crafts armed with missiles against US Navy fleet. Only better.
I have wrote a long reply but instead preffering to keep it short:
Iran adopts an anti-symmetrical doctrine, unsustainable, low on logistics and costs, replacable units.
While Indonesia adopts a conventional one, because the threat requires so.
Iran prepares their everything for short term offensive-defensive at the sea to inflict maximum damage on US assets who are fighting thousand miles away with a logistic matter, and long term defensive after a possible invasion.
While Indonesia faces China which fights within its own region, thus with ease on logistics.
While Iranian FACs run on domestic, cloned commercial systems avaliable in mass amounts, the hull made of commercially avaliable cheapest composites or polyurethane almost can be made at backyard of an house, costing 1/30th of the X18, while missiles again built domestically in Iran, costs 1/5 or maybe 10th of exocet-harpoon-NSM. Indonesia prefers top-notch systems which makes anti-symmetrical approach not feasible.
So Iran-Hormuz example is quite baseless.
And most of the modern naval radar systems are designed to operate well in cluttered areas, such as Smart-S and why it is chosen by Turkey, Greece or other countries, as well as, later by Indonesia. And China isn't a country lacking in tech, they have UAVs, MPAs.
While my point was, it is not feasible to move wheeled anti-ship coastal defenses around apart from the mainland, main islands, while this boat can reside on a small island for a day, then move to another. Literally acting as a mobile coastal defense skipping between beaches or islands, sneaking behind island,linked up to a MPA or UAV patrolling the region.
While the boat itself is not suitable to go out in hunting, would you drive a ferrari to a hunting in the wild, or would you prefer a jeep? You need a bigger FAC for that, like Chinese Houbei class.
However if X18 used as coastal defense, then in this case it will need a better endurance,more fuel for generators, galley-baths -berths etc. I know they can handle it, also officers can benefit from islands to supply their needs.
