For the heat transfer oil inlet of a thermal siphon reboiler, is it from top to bottom or from bottom to top?

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Continuous vacuum distillation column, with heat transfer oil as the heating medium. The company traditionally uses a tower reactor with internal coils for heating; the heat transfer oil enters from the top and exits from the bottom, with the exit located higher up (slightly above the inlet) to prevent the heating medium from not filling the coils completely. A reboiler is used (oil inlet temperature: 230°, oil outlet temperature: 215°, material temperature: 200°); we are still using the top-inside and bottom-out design at present. However, during discussions with the design institute, they said that entry from below and exit from above would also work. Personal opinion: With the heat transfer oil entering from below and exiting from above, it is equivalent to co-current flow; the heat transfer efficiency should be lower than that in the case of entry from above and exit from below, and a larger heat exchange area is required. I’m not sure whether both situations are possible or what’s going on Has anyone done similar designs before, or seen what happens in factories? Everyone is welcome to share their insights; thank you!~~~~