You must be using an old version (e.g. 6.1.3 or 6.1.2) because it was renamed from Default to Detailed some time ago.
Anyway, as I said, you won't see leff in the statistical parameters if it is not being statistically varied.
I was mistaken about annotating it on the schematic. The leff should be in the "output" parameters in the result browser - you can enter this expression in the calculator and then plot it (assuming you've saved family data on the Monte Carlo options form):
pv("/I7/M3" "leff" ?result 'output)
Note that /I7/M3 is the hierarchical path to the device in the schematic. If I do this, I see the effective length of that transistor versus the iteration number. In my case it doesn't vary because it's not a statistical parameter...