Cisco Firewall :: Tcp Flags And Timeout On ASA55XX 8.4(3)

I would like to understand someting about the behaviour of ASA with our traffic scenario and the management of  tcp sessions.
 
1) In particular we noticed that we have connections with the flags Fin without any acknowledgement. The session is silent (the bytes counters aren't incremented) but it remains in the session table as an established connection with the idle timeout of an established conn.
 
We have about 20%  (60K on 300K total) of conns in this state: at our eyes it seems to be an incorrect behaviour...
 
TCP OUTSIDE 62.149.128.151:110 INSIDE 10.254.158.12:61527, idle 0:11:36, bytes 433, flags UFIO
TCP OUTSIDE 17.151.0.200:443 INSIDE 10.254.229.94:52367, idle 0:01:25, bytes 4597, flags UfIO
TCP OUTSIDE 184.169.79.33:443 INSIDE 10.255.249.146:60143, idle 0:10:39, bytes 5590, flags UFIO
TCP OUTSIDE 157.55.235.158:80 INSIDE 10.170.37.102:62421, idle 0:00:53, bytes 1770, flags UfIO
 
2) On the connections considered as half -closed we have received an ack to the fin (r or R flag is present), we would like to set the idle timeout to a value lower than 5 minutes but we were not able to reach that result
 
timeout pat-xlate 0:00:30
timeout conn 0:10:00 half-closed 0:05:00 udp 0:02:00 icmp 0:00:02
!
access-list timeoutClass extended permit tcp any any eq www
access-list timeoutClass extended permit tcp any any eq 8080
class-map timeoutClass
match access-list timeoutClass
class timeoutClass
 
3) And this type of conns with a Fin on both side that I'm not able to understand... with an ack on one of the side how can I have the other fin??
 
TCP OUTSIDE 69.171.247.38:443 INSIDE 10.168.139.244:51236, idle 0:11:28, bytes 10536, flags UfFIO
TCP OUTSIDE 69.171.247.38:443 INSIDE 10.168.139.244:51234, idle 0:12:22, bytes 9070, flags UfFIO
TCP OUTSIDE 88.40.119.73:36962 INSIDE 10.255.93.162:36875, idle 0:13:27, bytes 3562, flags UfFIO