My oven was 20c higher than the setting on the pid controller when tested with a stand alone k type probe ' which is the best k type probes to use on these ovens please 

I find there is normally a bit of difference from what my thermo reads and the air temp of the oven. Any where between 6 and 22 degrees.
I do put the thermo in the vac bag, taped to the mould.  I use the exposed junction thermocouples. I wouldn't worry about it to much.
(Apologies if I've got the wrong end of the stick).