I believe that remote c-4 does count against the proximity mine count.But here's an interesting strat. Let's say you just come into a game or that you're infantry/vehicle cash is low or the buildings are gone. Use timed C-4 when you think there will be an attack soon and just keep restocking and throwing it on the floor as fast as you can. Basically you make it difficult and intimidating for the enemy to get in the building. Strange, but sometimes effective, and what the hell else are you going to do unless you have enough for a beacon anyway.