I've had too many Senegalus to count over the years, most of them WC, and most from Congo.
Of those they all pretty much varied in colour, size, head shape, body shape etc.
If I were to guess, I would still say Congo.
According to Dr. Shooks of the MOCA in Belgium, "Meridionalis" is most likely to have been a Senegalus from the Lake Turkana.
Turkana Senegalus get HUGE which is what MOST LIKELY caused this new "sub-species" Meridionalis to be started.
Here is a thread with pictures i made a while ago with the Turkana Senegalus that is currently being studied in MOCA. (Museum of central Africa, Belgium)
The fish was supplied to MOCA by the Karin and the guys from Big-In after one of there Kenya/Ethiopia expeditions.
Note the head shape of the fish being very different to all other Senegalus.
This is where it can get tricky too. Many of the Sens found in Lake Turkana appear to have head/body shapes the same as those found elsewhere.
These are thought to be Sens from Lake chad that have come through a tributary into the Lake Turkana.
Turkana local variants have this unique headshape such as the fish in the thread i linked to.
Remember the fish migrate, spawn and move all the time, so many of the Sens you find from Guinea are no different to those found in Congo or Nigeria.
http://www.monsterfishkeepers.com/forums/showthread.php?478225-We-need-more-of-these!!!