I meant FP Ginyu.
That was a way for the author to hide from us the fact that Ginyu could not access all Goku's power. In universe, it can be attributed to some sort of placebo effect.Ginyu did say that Goku's body was faster than his own after taking control of it.
Maybe he was under the same placebo effect too. Besides, would he ever dare to disagree with his superior?Wouldn't Jheese be able to tell if it was a placebo effect?