Lo, thine invocation's strength is proved!
But I am at work so more in a bit, being paged
Okay that took a while, here we go.
Reminder on how the

from raising knuffel works:
*Regular/elemental knuffel only!
-every level up divisible by 10 grants a bonus of 1k

-when you give up a knuffel for adoption, you get 100 : food: per level.
So a level 11 knuffel would give you 1k when you passed lvl 10 and 1.1k when you gave it up for adoption.
A level 36 knuffel would give you 3k from levels (1k each @10, 20, and 30) and 3.6k from giving it back to Knufftropolis.
Since it is much faster to level up knuffel to lower levels than it is to the higher ones, if you want to make food via knuffel raising it is easier and more efficient to do so by repeatedly raising them and returning them at lower levels than it is to raise them all the way to lvl 100.
Comparison:
50k xp needed for lvl 100. Cost of knuffel =2k, gain is 10k from levels and 10k from giving it up, total profit of 18k.
~4.4k xp needed for lvl 30. Cost of knuffel =2k, gain is 3k from levels and 3k from giving it up, total profit of 4k. Repeating this 11 times is 48.4k xp, and 44k profit.
So more than double the profit for still less xp than raising it all the way, once.
There are undoubtedly other cut off points and I am sure if you graphed it out the peak of efficiency is probably not at lvl 30 but that's sort of just where I ended up as my default.
So when I get regular knuffel still available in Knufftropolis, I like to raise them to 30, donate them back, and then get them again before properly raising them all the way to lvl 100.