We currently don't set any parameters for presentation (ppt) to HTML export, besides the PublishMode which needs to be 0 so that the Office server generates HTML files with embedded slide images. So we're using the default, which ATM means 800px slide images. I think this is OK for most of the cases, when there is not too much text on the slides. For edge cases the configuration can be adjusted to generate larger slide images.

For reference, the parameters that can be used are mentioned on https://forum.openoffice.org/en/forum/viewtopic.php?t=22655 (which points to http://pmwiki.org/pmwiki/uploads//Cookbook/DC.py.txt ).