Sirs 87 RON works fine on a R18, it is an average engine, nothing special.
Even the ultra high compression 9,000 RPM Rotary engine of a 05 RX8 creates maximum power at RON 95, having a 3 way cat converter and Euro IV certified.
My Mercedes M111 requires 90RON and 05 RX8 RON 95 but they also had a knock sensor and works fine on 87 RON.
If a petrol pump is good and without impurities, 87 RON is more than enough and using anything above is just a waste of money on Civic or Corolla, same could be said about using synthetics.
So unless the petrol is as cheap in Thailand as it is in Saudi Arabia or if the Thai R18 revs to 9,000 RPM, produces 250PS and has a compression ration of 11.7:1, there is no use for expensive petrol.
There is no harm in both physical injector cleaning or using an additive.
Physical flush machine has much better results.