Track dogs VS Cast dogs

Before I started making mine follow me out of big country off leash they all cast well, would usually go .5 to 1 mile which was just right for hunting sectioned country. These days they just go about 2 to 4 hundred yds.
In the last couple of years largely due to necessity of getting 4 to 8 of them out of big rough country by myself I started making them follow me out, sometimes even making them stay with me if we crossed another track, late in the day or getting too hot.. I thought they would catch on to going when I sent them and staying in when I asked them to, and they might if I was casting them more, but I have only "purely" casted them a small percentage of the time for the last couple of years.
Also they were hard to get to following me out, therefore took quite a lot of or a bit more severe correction which I am sure contributed to them being less apt to go without first smelling something.