Celestron Ultima 2x Barlow: Can you explain this?

My wife gave me as a present a "do not ever by this!" department store
70/700 scope wich came with 2 eyepieces, a Kellner 4mm an a SR 20mm.

The 4mm gave 175x which was over the recommended (140x) magnification
for the scope.

It realy hooked me into astronomy so I decided to buy a 11mm Televue
Plossl eypiece witch was a big improvement and today I bougth a
Celestron Ultima Barlow 2x.

The 11mm TV gave me 64x so with the barlow I shoud get 128x which
should be just fine for the apperture.

BUT when I try the 11mm TV with the Barlow on Mars I get a BIGGER
planetary disk than with the 4mm eyepiece. I can tell this because
with my other eye I can compare the planet to the holes on the tripod.
And yes I put the barlow after the diagonal.

What happens here? I suppose 175x is bigger than 128x. Is this right?
What am I missing?