The problem is, many of the "standard" works start with the assumption that Mars has readily accessible subsurface liquid water, and they adjust the models to fit that idea.

Instead, if you start with an objective model, and work forward, you get a deep-frozen planet.

If you imagine that Mars is identical to Earth, but smaller (the Earth-like approach), you would get a heat flow less than the Earth's, because there is more surface-area to volume ratio for a smaller planet. (Mars is 1/2 the radius, 1/8 the volume, and 1/4 the surface area, so 1/2 the heat flow)

You also lose heatflow because Mars is demonstrably lighter (less average density) than Earth (only 1/10 the mass, not 1/8), because its composition is (theoretically) different from Earth's, and because it has a different heat-flow history and fractionation of radiogenic elements near the surface.

This field is overdue for a review, but I had a paper knocked back a few years ago because it was perhaps too critical of the orthodoxy. it needs someone more objective and less cynical to write the paper. There are a lot of recent papers on small aspects of this, but nothing that gathers it all together.