More to the point, isolators simply choke off the rf flowing on the outside of the coax and have no effect on whatever rf is flowing inside that coax. Isolators are also often frequency dependent insofar as their maximum effectiveness goes.
Some that work spectacularly at hf fail at vhf and above, those mixed for best response at vhf and above are seldom useful at hf. I've mixed isolator ferrites for a broader response, for example, using 43 mix as well as type 6 and/or type 4.