Do fractional circuits generally underperform compared to full circuits

I will admit this is entirely anecdotal, but it seems that fractional circuits (e.g. 200mb, 500mb) seem to always underperform, while full circuits (e.g 100mb FastE or 1000mb GigE) actually perform pretty close to their theoretical max.

Unless I am imagining the above entirely, I assume it has something to do with the QOS/traffic shaping that goes into provisioning these fractional circuits?