It depends on the election. It is difficult to estimate the number of voters based on whether the votes were cast abroad or by proxy in France.
I would simply like to correct what Professor Frank just said. During a legislative election, for instance, French citizens may choose to vote in France for a member from their riding. They are not required to vote for the riding abroad. They choose their representation.
The levels are higher for presidential elections, obviously. Voter turnout is very high for elections for the president of the Republic. We're talking about over 50% of French citizens abroad.