I've been caught up trying to ID an adult yellow-legged gull in Uganda via inaturalist.org. The observer initially suggested it might be michahellis, which I felt wasn't the case: out of range (?), bill too fine and the bird doesn't look square enough, somehow. Another opinion was voiced for fuscus graellsii, but that also doesn't seem right to me: even with bright African sunshine, the mantle seems too pale and again the head/bill structure appear wrong. I was tentatively heading down the route of heuglini or barabensis, but without real-life experience of either taxon I'm floundering somewhat. If anyone has an opinion on this bird and can give me some ID pointers I'd be really grateful. Even if it shows I'm just being a muppet

The background details to go with the photos (I have asked for and received permission to use them

Many thanks for any and all help!
Jeremy