Internal meter question...

I recently checked some antenna's on a truck thinking they were suspect. Not sure of the brand but they were dual 4' with an allen head set screw to hold adjustment of the wire.. The radio is a Cobra 25. Anyways the internal meter ( I know not to trust it) would read about 2 when keyed up. When i checked it against an external meter, swr was actually 4-6 dependent on channel. Needed to shorten the antenna's but they were all the way down.
So I put dual 3' firesticks on and got the swr on the external meter down in the 1.5-1.75. What's odd is that now the internal meter reads 4.5 or higher... Anything in particular that would cause this type of result?? Or is it just one of those things??