Update II: I assume it varies on how big the source file is as I'm playing from memory. . .
It will vary depending on the amount of data in the audio engine, so higher-complexity files (higher sample rates) will increase memory usage. If you're playing from memory, the impact will be greater (up to the limit that MC will allocate for this purpose).
File format (FLAC vs MP3) should have a negligible impact because it is decoding to PCM in either case.
Other DSP settings, especially convolution filters and upsampling, can increase memory usage.
In any case, I don't think 212MB working set is
especially huge on a modern PC, that probably has 4GB of RAM on the lower end. It is higher than I'm seeing, but I don't know what DSP settings or output settings you're using. But as I type this, Firefox has a nearly 1/2GB working set, so... I suppose it is relative.