heap_size capacity vs len

[faassen]

I just was reading vers-vecs documentation and it says this for its heap_size:

This does not include allocated space that is not used (e.g. by the allocation behavior of Vec).

And indeed in the code I can see that vec len() is used rather than capacity. Should we match this reporting? It's I think a more accurate description of the data used, unless the capacity allocation is inevitable (but since RsVec is constructed from a bit vector it probably has a capacity identical to what's required).