Even though the distance across the strait is very small, Taiwanese radar would nonetheless be able to give the ROCAF a few minutes notice preceding such a strike. ROCAF aircraft would be scrambled, and greatly complicate matters for Chinese strike aircraft performing their SEAD missions.
During Operation Focus, the IDF Air Force was able to achieve full surprise only because 1) the Egyptian Air Force had ordered all radar stations to be shut off 2) IDF aircraft flew out across the Mediterranean before heading towards Egyptian airspace, thus avoiding the main concentrations of Egyptian radar stations. Also, the Egyptian Air Force as a whole was in a low state of readiness. In the case of rising tensions across the strait, the ROCAF would no doubt be flying CAPs and have all radar and air defense sites on wartime alert.