This pic is from behind Mike's regiments which are the blue and red ones towards the lower left. His blue regiment is about to charge my blue regiment which is falling off the left hand side. I have a falconet either side of the regiment angled inwards as shown in the next two pictures.
Well, if the gun is angled as you mentioned in the diagram I suppose that the gun could fire traversing fire. However, it is all a bit odd to me. I have never known anyone claim traversing fire from a gun in a position as you describe in your original diagram. Look at "Closing Fire with Cannons" on pafe 51, it describes the situation you have given us. Of course, there is the other thing to consider. A unit can only fire out of sequence once. So if the cannon were to use traversing fire and was then attacked itself, it could not give closing fire to defend itself and guns tend to die when caught in combat. It's what skirmishers are good for.
The gun will be in combat and so cannot give support to the infantry, which can help the charging unit. Remember the definites that you can rely on. Units in support of a combat give +1 to resolution. Closing fire does not, although any casualties caused will modify a break test roll. Closing fire, and traversing for that matter, may not cause any casualties at all and you must roll for the closing fire from the gun seperately because these have a negative modifier on any resultant Break Test.