Had the original silca frame pump eons ago that had the campy metal head w two prongs coated in rubber as well as a pump w plastic head. The current version is like the latter and my top tube was sized for a large pump.
I found the head of the pump slid down the head tube no matter the orientation of the pump. This was within a minute of install....no riding required. I called Silca support. No suggestion other than go one size up but...the new pump may not compress enough to fit the top tube. Of course that is what happened.
I don't think such an expensive product ought to have this issue. Bike is classic geometry.
I stuck on some handlebar gel at the junctions and the issue is fixed. I would have sourced an old campy head but pictures didn't show it would fit the pump.
Have not tried the pump but expect it to be good like in the olden days.