[DS2] Defender/Attacker ratios and fixed defenses

Now, we've all heard the old saw about requiring 3:1 to attack a fixed
defense. 

This is (somewhat) a real life truism (or a reasonable rule of thumb).
Depending on the defense, of course, this changes. 

But what are fair numbers in DS2 for an interesting game? 

What are fair benefits to accord the defenders? 

How significant should mines and other obstacles be considered to be? 

I'm guessing that some benefits a defender might receive:
Registered batteries (faster/less deviation)
Minefields (and fake ones) as a channeling tool 
Obstacles as another channeling tool (concertina, tank obstacles, etc)
Trenches with overhead protect
Bunkers
Selection of useful terrain to channelize or deny passage to enemy
forces
Registered ranges (staked, or by features) to allow better infantry fire
Tank revetments to allow tanks to be hull or turret down (and other
AFVs)
Berms or dirt walls
Intelligence on attacking forces (qty and mix)
TacAir

Attackers:
Intelligence on minefields and other channelizing obstacles
Intelligence on defending forces (qty and mix)
Location of enemy bunkers/etc
Artillery (guns, rockets and mortars)
Engineers/Assault Pioneers with appropriate obstacle reduction equipment
Scouts
TacAir
Armour and other mobile forces to allow exploitations of breaches

First question is are any of these things not represented in the DS2
rules well? 

Second question, is 3:1 really a reasonable attacker ratio for a fun
game in DS2 against a prepared defense?

Now, I know a scenario has to be balanced to some extent by eye in these
cases because the efficacy of a defense has a lot to do with what types
of units are attacking, how many, what type of artillery, etc are
present. And the presence of any defender reserves. But some ballpark
idea of fun force balance must exist in the community... clearly a
number of you have played large games....

So, thoughts?