The PLAN will be able to mass a lot more Type 056s than the ROCN can field SSPs.
Skywatcher, I already made the point that if the PLAN was establishing a naval blockade, ships heading to Taiwan would not disclose that they were going there. There are so many ports in the area, it would be pretty easy to hide the final destination (or even just an interim stop in Taiwan).
Second, can you please tell me, what makes you think that Taiwan-bound ships will file in an orderly queue towards PLAN vessels? The PLAN can't board every single vessel heading for East/SE Asia on the off-chance one is heading for Taiwan.
Additionally, if those SSPs are off dodging ASW while trying to find the PLAN's far blockade, then they can't do anything about amphibious landings, not to mention the close blockade.
If China starts an invasion of Taiwan there will be little point in establishing a far blockade because few merchant ships will be sailing into a warzone unless they're heavily escorted. The conflict would probably be over in less than a month, one way or another.
Also, if China starts a far blockade it's going to tip its hand that it's quite possible an invasion will start. In any event I doubt Taiwan would send all its submarines out to try to break a blockade, not least because it would only need to break it in one place.
You could also, perhaps, address my point about the USN being able to attack Chinese shipping with plausible deniability due to using the same weapons that Taiwan has.
Another thing: you can enforce a blockade with MPAs and UCAS now.
First, where are these aircraft going to be operating from? China doesn't have the wide range of airbases that the US or even UK does.
Second, how on earth are they going to assess where a ship is going? They could identify that a vessel was in a particular location and its heading, but that's it. China can't just blow ships up because it suspects they might eventually go to Taiwan.
Unless the ROCN suddenly becomes clairvoyant, they won't be able to predict where the PLAN task force will be going while the SSP is in transit.
As I've pointed out, the PLAN would have to spread its net fairly wide to stop ships getting to Taiwan. The PLAN can't choose where to intercept ships, because it won't easily know if they're headed for Taiwan. It will have to split up into small groups, probably just a couple of frigates or destroyers, to patrol certain sectors.
Also, there's the very simple fact that if Taiwan is expecting important deliveries then there's nothing to stop its submarines going to meet the ship(s) in transit and then escort them on the way in. Even if somehow China can find out if a ship is going to Taiwan, the Taiwanese government is going to know beforehand.
Back to the smaller submarines, even if we ignore the far blockade, what would stop the PLAN from sinking them with its ASW platforms? Smaller submarines will have a shorter range, which would make it easier for the PLAN to concentrate its ASW efforts.
Anyway, the discussion is academic. The submarines' size has been fixed, and Taiwan isn't going to build smaller ones.