OK, maybe you'll try to explain. Let's first consider dependency on L. So PoW difficulty to generate an envelope depends on current number of tips. And the device probably doesn't even know that number. Why does it depend? In Bitcoin and its clones for example difficulty doesn't depend on tps rate or whatever parameter that could be comparable to the number of tips in the DAG.
It depends because some work on finding optimal 2 tips is done.
Do you mean that a node should traverse more or less the whole DAG to detect doublespends and choose tips that confirm more confirmed doublespends?