I think you are mistaking the numbers for the component heat exchanger and the overclocked heat vent.
OC vent takes 32 heat from the core
Comp Heat Exchanger moves 36 heat around
The planner v3 is still up to date with the calculations in existing reactors.
You have to move 8 heat from the left OC vent to the bottom OC vent
You have to move 8 heat from the top OC vent to the bottom one. There is no direct connection so you move those 8 heat to the right OC vent.
The right OC vent gets an additional 8 heat and now has to move 16 heat to the bottom OC vent. normal heat exchangers can only take 12 heat, so you need an advanced heat exchanger or a component heat exchanger in the bottom right to move those 16 heat to the bottom OC vent.
The bottom OC vent gets 8 heat from the left and 16 from the right OC vent, 24 in total. 20 of that is cooled by itself and 4 by the component heat vent.
if you have no heat exchanger in the bottom right, the bottom vent will cool 12 heat because the heat exchanger will move 12 heat from the left to the bottom OC vent. this is because there is no equilibrium between heat generated and cooled and the system would fail in the future. The values that are displayed by the planner are more or less average values because the reactor doesn't behave the same every tick. heat gets moved around all the time and so the heat that is generated each tick rises or falls depending on the current state but when the planner says it will do a full cycle, the system is stable