How are you getting ur cranks deeper? leadcore? snap weights?
I do both actually. Some days it seems like they bite leadcore vs fireline, not sure why. My choice however, on using lead core vs snap weights depends on some variables. Size of lure, depth I'm trying to achieve, speed, and how many boats are in the area. For example, if I'm in a crowded area say 30' deep trying to get #5's down there, I could let out 180' of line(lead core+leader) or I could put on a 3oz snap weight and maybe only need 50-60' of line out.
I also find that in late summer as we get hot water temps like we do now, speed kills. lead core limits how fast you can go. I like 2 or 3oz snap weights because I can kick up the speed to 2.5-3mph and still keep my baits down without having to let out a huge amount of line.
The other option of course is to go with a bigger crank like a reef runner 800 or flicker minnow #11. I think on the dive curve from Precision Trolling, it take close to 200' of line to get a reef runner down 30'. Add that 3oz snap weight about 20-30' in front of that bait and now you only need maybe 60'(not sure the exact amount), but you see my point.
Lead core and snap weight both are fun and help me get more fish in the boat, and if you implement them, with some practice you will see the pro's and cons in both. Each have their own situation that they shine.