Flat finite elements require a lot of tiny facets to wrap around curved shapes without losing mass or surface area, even when the temperature gradients aren't large enough to justify all those elements.
Using Sinaps? It is not too soon to get started with TD/FloCAD!
Thermal Desktop (TD) is fully parametric: any input can be specified as a function of almost anything, including outputs. TD also accepts arbitrarily complex co-solved customizations.