My uncle was a very high ranking official in a government back home for two or three years and his son told me his official income was less than $1000 a month but his lifestyle wasn't anywhere near that amount. He took us to restaurants at hotels every night where a plate costs $15 each (there was like 7-8 of us nephews and his daughters and sons).
But there's more to it then the income they receive. I lost count the amount of goats he was always given by his reer baadiye clansmen and guests who came to the house with unlimited bundles of khat or when wealthy people paid for his gas or when shopkeepers(who I assume was also distant relatives) would tell us to take candy or chocolate of drinks without writing down what we took. Or when internet cafes gave us free unlimited slow speeds.
Of course he obviously did stuff for them in return. Probably giving them small plots of government land or something.
What I am getting at here is the invisible incentives and free stuff and bribes Hassan Sheikh gets from locals or rich clansmen could probably exceed his official income. This is not including the money he steals