Just noticed in a new career that the MHS adds 1.25 tons when going from 1.25m Medium to Heavy. This is about 2x the weight of the Mk1pod + MHS Medium. Not counting ablator which doesn't add a lot to the total.

Is this intentional?

Increased mass is intended, and yes, I believe the 'heavy' should have about 2x the 'dry mass' when compared to the 'medium'.

Now... that isn't to say that the starting values are correct... bad base value = bad derived values....

IRL heat shields loose very little mass - most of the ablative material stays attached but charred.

I've simplified/unified the mass and volume calcuations for the ModularHeatShield (both module, and part) for the 1.4 rework.

Mass and volume are now calculated from the model definition specifications for mass/volume, current scale, and selected shield type. Scaling for mass/volume now follows the standard cubic scaling used by the model-definition system, but might be made configurable to square-scaling if the balance deems it necessary.

These stats are -also- used when the module is applied to an existing part, though no model or fairing manipulation is done ('currentDiameter' should be specified in the config to match the actual part diameter). This should allow, in theory, for a single unified set of stats to be used for the heat shields regardless of if it is integrated into a part, or used as a stand-alone. (I'm sure KSPs simplified thermo model will mandate some per-part balancing though...)