That's because front JPJ requirement is 70% VLT (visible light transmission), sides and rear can lower to 30%.

IR is not the ONLY heat from the sun, all the other spectrums also transmit energy which you feel as heat finally. So IRR (Infra-Red Rejection) is not the ONLY spec you need to look for.
If possible ask for the T-SER value, i.e TOTAL- Solar Energy Rejection, and this value normally not that high. I think highest I saw is 60% TSER being advertised, don't know if got higher.

Malaysia so hot, nothing much you can do, tint helps but not by much if you park your car in the hot sun from morning to evening as in when you go to work.
Generally the darker tints performs better to help reduce how fast the car heats up.

Also tint is where accessories shop earn the most money, I don't believe the very expensive branded tints are so much different than generic GOOD tints.
For all my cars, I don't use the cheap tints, nor do I use the expensive tints, I find the mid-range tints are good enough and perform just as well as those RM2K-4K tints

put another layer of tint.

then u just need to find the right balance of acceptable VLT vs how dark you wanna tint