The passes behind the LOS is driving me crazy too. I keep thinking it's ultra restrictive and then a QB starts throwing it again. You might be right, I may just need to completely eliminate passes to a receiver behind the LOS, period, until I start building the screen pass logic.
The drops are being counted if the ball is within the catchability of a player, but here's the current weight of each factor in determining whether a pass is dropped or not:
60% base chance of a completion
2% for above his head - higher above the head, the less lower this value. (Ball must be within a catchable height to get here)
2% for how close the ball is to the player - further away reduces this value.
20% - pass catching bar
3% - experience/fatigue
2% - if the ball is behind the WR there is a 2% penalty
11% - coverage - this is a calculation based on the number of defenders right on the WR and how our courage stacks up against their punish receiver skills.
So, a 100 pass catching bar gives you an 80% chance base, the other 20% are influenced by other factors. The most likely reason for high pass catching bars to have drops is probably the coverage around him.