Personally i see no different in digging location, i got mole cricket and rhino larvae pretty much everywhere,on jetty or even from a rock.
when u hit 100%, mole cricket(95%) will become more easy to get,and concafer (90%) obviously much more easy
digging is super random, i dig like 50 times and get nothing no mole cricket or rhino, next 20 dig 2 moles and 2 rhinos
i see no different for the last 5%,maybe much more easy (just my opinion,no data to support that statement,like a reward from developer for reaching the end of bait harvest,haha), and crayfish tail, river mussel and zebra musssel are much more easy to get than rhino because u can target those bait fishing at volhkov.there is no size limit for crayfish and mussels to turn into bait.u just need 4900 silver professional knife and it really worth to buy.
p/s i hope u can understand what i wrote,english not my 1st language and gl mate