The company I have worked for supposedly has a policy that there is one rig supervisor for each pulling unit. In reality - there are often 2-3 rigs per supervisor.
I have heard about companies having approximately 100 wells / production engineer when the wells are new. Though, some companies are running in the 600-1000 wells / production engineer range.
I expected the higher well count / engineer are for fields where the conditions are more stable and not where there are lots of artificial lift changes and workover operations needed.