Hi Hookbill,
really nice thread, I like the maps a lot!
a while back there was some discussion on Himling (the island that appears on some maps) ie Himring, which may or may not be a third age survival of Beleriand.
See here-
(unsurprisingly the canonicity is disputed
)
BD thread on remains of Beleriand
Typically the old link to the map discussed on that thread is dead and I could only find a diagram online - scroll down to the bottom--
Diagram
After a little more searching, here's the Encyclopaedia of Arda's take on it,
Where in Middle Earth was Beleriand?
Looks pretty close to yours, but if you believe the canonicity this should be the key.
After a bit more of a stare, maybe your Beleriand needs to shrink a bit?