OK, so I tried to turn the info of the OT into an OSSC profile, see attacked zipped json, for v0.83 of the firmware, to be imported in the OSSC profiles web site
http://pbnl.byethost7.com/ossc/profiles/.. BTW it also includes a Sharp X68000 profile.
Since I'm still not fully understanding this OSSC, for all the Amiga resolutions that each map to 240p/288p I applied the advanced timing tweaker settings to both 240p & 288p. Maybe somebody can tell me which of the two is actually used, 240p or 288p?