Although I wouldn't recommend using the wysiwyg; a quick way around this, so that you can have your own font sizes within the wysiwyg editor, would be to change these two .js files below...
skin1/modules/HTML_Editor/editor.js
skin1/modules/HTML_Editor/moz/editor.js
and locate these lines of code in both of them...
Code:
if(f.size==1)nSize="8pt";
else if(f.size==2)nSize="10pt";
else if(f.size==3)nSize="12pt";
else if(f.size==4)nSize="14pt";
else if(f.size==5)nSize="18pt";
else if(f.size==6)nSize="24pt";
else if(f.size>=7)nSize="36pt";
and change them to the size you like, for instance (these sizes below are NOT in relation to the equivalent size in pt's)...
Code:
if(f.size==1)nSize="0.8em";
else if(f.size==2)nSize="0.9em";
else if(f.size==3)nSize="1em";
else if(f.size==4)nSize="1.2em";
else if(f.size==5)nSize="1.4em";
else if(f.size==6)nSize="1.6em";
else if(f.size>=7)nSize="2.0em";
I haven't tested this thoroughly but it doesn't appear to be conflicting with anything else within the js and outputs just the same. The em's I have introduced to show that over units are possible. You could just as easily swap...
else if(f.size==3)nSize="12pt";
to else if(f.size==3)nSize="11pt";
...if needs be - for size 3 to come up as 11pt's.
Hope this helps.