Apart from the amount of carbs, there's also the speed of digestion, and hitting the bloodstream.
Spaghetti for instance is notorious for raising BG slowly and very prolonged, so if you're testing at the 2 hour mark you might miss what it's doing in the next 4 hours.
With the apples it may be you're catching the peak of the spike where the peaches may spike quicker, and you're testing when it's on the way down again.
A lot may depend on what else, if anything, you've eaten
I have absolutely no idea if this is what you're seeing, but it might be a factor.
You say you use a sensor, are you seeing any patterns telling you more?