I found the same with Ashley really.  You have no other choice but to increase the dose really though when they are babies because they have a less robust immunity--and especially if your not breastfeeding.  (I did not breastfeed Ashley as I gave up after day 4 or 5 as he seemed to be disinterested in it and I switched him to formula.)  As it was I thought a few days later that he had an allergy to the formula because he then seemed to drink even less due to the CAH.  

He scarcely was ill during his toddler years and when he was the doubling of hydrocortisone always meant he coped better with illness than his sister Chloe I found.  As he has grown older his immune system has improved greatly.  It usual takes something really nasty to knock him over.  The advantage of having other kids I guess is that you see bugs and flu’s and stuff go through a few kids first and then the minute he shows symptoms like scratchy throat, I double up immediately.  I feel it is better to do that than let him get to the stage where he get’s a chest or synus infection or worse.  It often means just a short snap on double dosing for a day and half and then we go back down to normal dosing.  He always recovers faster than anyone else in the family where coughs and colds are concerned because of this I feel. 

With the exception of the last illness I have always had advance warning with another child coming down with illness first.  the last illness was out of the blue and he must have been the first one to come down with it so things had got a good foot hold.  The hit to the head also made him nauseous and he looked quite sick but even then I did not double his med’s as at the time he had no temp and I felt he may have been just a little winded from being hit with the ball.  So initially I just gave pamol for the headache.  However later in the day, he was not much better so I brought the 2am dose forwards and increased it.  

I think a lot of the time as they get older the whole thing becomes a lot easier and you can sort of gauge whether to double or triple.  I never start of with triple unless  feel doubling was not enough.  I go by the nauseaous feeling these days.  I can gauge within an hour of him taking his med’s that if he still feels nauseous, he needs more.  If he vomits before that of course he get’s the dose repeated but in triple amount and I get him to lie in the recovery postion with a towel under his head because he hates to be upright when he feels nauseous.   If the triple dose works and is kept down, the next dose is given at triple also.  When he get’s to the stage where he wants to get up and move around and is looking better and feeling better and the temp is down, I usually decide at that point that we can go to double dosing again.  It just seems to have become more of a refined thing as he has got older.  there are times when he has felt nauseous and i have doibled then tripled and he has been out playing in the street some hours later and was well enough to be dropped down to normal dosing the following day.  I guess it depends how things are and the type of illness and how quick you are to act half the time.  Because when they vomit and lose fluids they are really needing triple dosing I feel as they can absorb a little of this before it reaches the small intestine. 

My concerns about injury though was that the small amounts that are absorbed at those times are simply not in a great enough volume to deal with the severity of things.

You sound as if you have it all down pat anyway and I definately know it does get easier, but I really feel a whole lot better with a kit in the cupboard.  I have never used it but I know how now and it is just our safety net.