In my rantings I'm almost exclusively talking about Concentration to cast a spell, not the rolls every two minutes for when a D:Conc spell is active.
Okay sure, there is Confidence. But those points are limited in number, and require you to actually gain some. If the SG remembers to award them (which may not happen, especially if players forget to use them), if you burn through 3-4 in a single encounter this is IMHO not sustainable, unless your SG dishes out a lot more than we're used to. Self Confident may be a popular choice for that extra oomph when it really matters but it is still a an active choice and not all magi have this.
Being injured requires a Stm+Concentration of 15. Assuming an average die roll of 5 plus Confidence your Stm + Concentration still needs to be 7. Actually even higher, since that injury surely inflicts Wound Penalty on you and thus modifies the roll. Sure, you're not injured every round, but other rounds you may be dodging to avoid getting hit which is still an EF of 12. Since you can't be using Confidence every round this gives similar numbers.
Note that the table also has an entry for sudden noise of flash of light, and this I assume means things that actually surprise you. So that the magus you're fighting casts BoAF is expected, but if his servant sneaks up behind you with a device of BoAF...
I'm not really questioning the rules for Concentration Rolls - well a little - but mostly asking how many people enforce this and what their experiences are?
What is the Concentration score of your combat magi?
As additional information I point towards Normandy Tribunal's bad-ass magus Rotigers of Tremere - Montverde's chief combat magus. IIRC his Concentration is 3.
It seems to me a magus, barring one protected quite well by a Shield Grog or one with high Concentration ability, is likely to fail casting spells quote often. A magus designed towards combat and action is likely to have a positive Stm since he is likely to want to pull off his spells with a decent Penetration, and this helps with Concentration as well with Soak. He is advised to prioritize Concentration ability however, and perhaps to keep training to lower the odds of missing out on a round of casting. Ease Factors do not increase for the more challenging encounters with more powerful beasts or persons, although increased ability scores or better powers may be harder to avoid and therefore increase the frequency of being hit.
Luckily Concentration is a General Ability so books on the subject may be bought with merely vulgar silver rather than precious vis.
Oh, and how do people view Concentration rolls for Fast-Cast Defenses? Are they required if you've recently been injured or are dodging?
Titus of Flambeau and his party are traveling through Schwarzwald to get to Durenmar, when suddenly they are ambushed by a group of Zee Nazty Bockmänner!
Bockmänner win the Init witn 18 vs. Titus' 7.
Count 18: Bockmänner charge in for an attack.
Titus reacts with a Fast-Cast spell to block off his attackers. He does not need to roll Concentration since there is no distraction, and this is Fast-Cast not a regular spell being cast, which takes several seconds. It works but only one of the two Bockmänner is blocked, leaving the other to attack. This attack is succesful and Titus injured.
Count 7: Titus cast a spell but needs to make a Concentration roll of 15, since he was injured. This is a hard roll to make.
Count 18: Bockmann attacks, if Titus wants to try another Fast-Cast defence does need to roll Concentration for being injured? He was injured last round, but because Initiative is an abstraction of actions of about 6 seconds happening more or less simultaneously or at least with overlap. Is the injury a distraction from the time of the Bockmann's attack in Round 1 over the course of anything happening up to the time of the Bockmann's action in Round 2?
Anyway, assume Titus is hit again.
Count 7: Titus now needs another Concentration roll because he was just injured. Again. Since Concentration rolls have no exceptions from Wound Penalties these rolls quickly become more and more difficult to pull off. Actually, the table for Continuing Situaitons special rules here only for injuries, which IMHO implies they are used normally for other Conc rolls.
Even if Titus has not been injured he would still have had to roll vs. a 12 for dodging. Otherwise he was sure to have been injured. Of course, a Fast-Cast defence could have blocked the attack so he would neither have been dodging nor injured thus avoiding Concentration rolls. Or he could have used a [strike]meat shield[/strike] Shield Grog as Defender and also avoided this. Against formidable opponents a Shield Grog can also quickly be worn down by Wound Penalties, but at least it buys the magus some time to cast spells with a lot less distraction and hopefully dealing with the situation.