It’s an issue that has been experienced with HeavyM 1.11 and below by Microsoft Surface users in particular, and it is due to a dpi (dots per inches) difference between the displays. This problem can be solved with the adjustments suggested for interface display issues (see related topic).
Otherwise, it can also be corrected by adjusting the position and size of the projection manually in the HeavyM menu Projection → Parameters (these are HeavyM 1 features and only unlocked in HeavyM Live). In these settings, you are able to change the width, height, and X and Y-coordinates of the output.
Note: if you are using HeavyM 2 and this happens, please submit a report with details about your configuration.