the reason for this is because, for most people, for most diets, if the carb ratios and basal rates are "good" the total insulin comes out ~about~ 50/50 (basal:bolus)
it's not to be taken literally, it's a guideline. it's not an absolute, it is an average of average averages.
I had excellent control (a1c 6.4%) with basal - to - bolus ratio of 25 75. what did this mean? well it means that with respect to the average, my carb ratios were too high and my basal rate was too low.
I re-checked these numbers and found out that in fact... my carb ratios WERE too high. for 6-7 months I was on a regular routine, I ate pretty much the same meals and the same amounts at each meal, and I was taking too much bolus, for my carbs, and then too little basal to offest an overdose at meal time. My numbers were great, but it's still not perfect pump tuning.
the only real thing that was not good for me was these 2 things: if I fasted, my blood sugars would rise. If I varies my meals, my blood sugars would be more unpredictable.
So I started there, and re-cast my basal rates, then re-figured my ratios and now on any given day I am somewhere between 40-60 to 60-40 and I have a much more flexible pump program. I can fast, I can have 100 carbs for breakfast, and the outcomes are very much more predictable than before (and that's all).