1. Everytime I play a deathmatch against another person online, my percentage (shown in the lobby) goes down by 1 percent. What is this percentage and how can I lower or increase it?

2. I win a lot of deatmatches (I mostly host the game and select playing for points), but my points shown at 'Hard Cases' stay at 599 and my ranking never increases. When I play a deathmatch, I often win the first round or the first and the second round and then the other player quits or I quit. Should I finish 3 rounds or something to increase my ranking or can I just stop whenever I want and still increase my ranking?

Thanks already.

It's the percentage of your last 100 games that ended successfully. If it goes down, it means the game disconnected (either you or your opponent).

I'm not sure about the other problem, I stopped playing the PSP version. At one point it wasn't saving stats for any of my games but that was fixed.