I think this can be a very individual thing, perhaps different metabolisms process them more or less efficiently.
I myself can eat lentils by the KG and i don't see a spike, others have a tiny amount and get a large rise.
Note this is from a Type 2 perspective, but i would guess the same differences in conversion rates apply to type 1, though if your not sure how many grams of carbs your getting out of them it makes it very difficult to guess your insulin requirements.