@arnoldbeilandevozon,
I am afraid, the positioning of the frame in HTML cannot be improved, because frames with text wrapping are not fully supported in HTML documents. The solution is to use Html Fixed file format:
Document doc = new Document("C:\\temp\\FramesLost_input_output_code\\frames_lost_input_file.odt");
HtmlFixedSaveOptions options = new HtmlFixedSaveOptions();
doc.Save("C:\\Temp\\FramesLost_input_output_code\\21.3 fixed.html", options);
Secondly, you’re right, frame’s bottom border is missing in output HTML. To address this problem, we have logged a separate issue with ID WORDSNET-20892. We will keep you updated on the status of correction. We apologize for your inconvenience.