In fact it's the other way around: OSD-position allows the OSD to shrink, so it will fit on your telly in case overscan is used. Enlarging OSD is not possible.
It is indeed a pity that the default PLi-HD skin leaves an enormous area all around unused. There are several screens (channel selection/movie selection/EPG) that really could make good use of all available space.
Enlarging is possible! The only thing OSD position plugin do is enlarging. it enlarges the OSD from the native size. Thats why the quality of the Skins is very very bad. Picons are also enlarged and is also the reason picons look very very bad in infobar and channelselection. Thats the reason
If I uninstall OSD position plugin, then I have the native size on the screen and all is sharp. the picons are sharp as they should be.
If I have set 1080 in AV Settings and on my TV no overscan (like 16:9) then natively is 1280x720 smaller than the screen. OSD position do only enlarge the native size to the screen size.
But everybody can try. Uninstall OSD position plugin, then you will see sharp skin, sharp picons and sharp fonts.
The best way is 1920x1080 for skins so they match the size of the screen, I used on dmm images with dreambox my own 1920x1080 skin. it worked well, better then 98% of the skins with kitch graphics, but hbbtv sucks with 1280x720 and is the only thing that makes professional designs and skinning impossible on enigma2. If HBBTV could work with 1920x1080, then it were the problem solved.
But now if you like sharp skin, the size must be 13...x8... and uninstall the OSD position plugin because this plugin enlarges the OSD and makes it unsharp.