The anime ends at a specific point in the manga, but it's a bit hard to pinpoint exactly without looking at both side by side. You might have to do some comparing yourself to figure it out precisely.
I really like 'A Different Path'. This fanfic takes a unique turn by changing some of the events in the original story. It shows an alternate version of Moriarty's plan and how it affects the other characters. The writing style is engaging, and it keeps you hooked from start to finish.
A good 'Moriarty the Patriot' fanfic should first and foremost stay true to the characters. For example, Moriarty is a complex character with his own motives and beliefs, and any deviation from that without proper explanation can make the fanfic feel off. Also, the plot should be engaging. It could be an alternate take on the story or a deeper exploration of a certain aspect like the relationship between Moriarty and his brothers.