Stacking barlow lens

Has any one tried to stack 2 or more of todays short barlows? would two 2x = a 4x ??
Or Would placement be a factor. and would there be other prohibitive reason for not doing this???
So many questions

I stack 2x Ultima and 2.8 Klee on occassion (Lunar only). If Klee is on bottom of stack image is awful, if Ultima is on bottom much better image. I've done this stack with a 5mm Ep and acceptable image for Moon. ...and by "acceptable" I mean lots bigger image scale, softer image, loss of some details, but still a pleasing view. Sometimes it's interesting to just feel "closer" and like "being there" regardless if you lost some details