Riding increases the pressure in tires due to road friction in any weather, and due to contact with the hot pavement in the summer months. If you set them cold they're good, don't worry about them hot, nobody ever did before TPMS were invented, and nobody ever had issues.
If you insist on taking a mathematical approach, just remember that the internal tire pressure is not what the gauge reads, but rather the gauge reading plus 15, because atmospheric pressure is about 15psi at sea level. So, if you have it set to 42psi cold on the gauge, the internal pressure is 57psi. If that increases by 10%, you add 6psi, not 4psi.