Its very random.

My perception with food is 170+ and when I was farming astral rock there was a day i had 3-4 in an hr then nothing for couple of hours. On some days I get 1 per hour.

Same with DS and Cobalt. Sometimes I hit 1-3 HQ per node and sometimes I hit none for a long time.

Hopefully with my new militia sledgehammer the results will be better