Yes, cash upgrades mostly appear after miles upgrades disappear. Cash upgrades IS NOT done automatically but is the manual decision by TK staff (I was told of the destination, but not sure). Sometimes the cash upgrades are turned on early-on and you will see miles and cash upgrades simultaneously. The more popular routes are more likely to have cash and miles upgrades offered simultaneously or even just cash upgrades being offered (defenitely all of my USA to/from flights on TK were cash only upgrades).