DIYbanter - Anyone help with water feature problems

Installed a water feature for the missus. It's essentially a 2 foot
high gargoyle that spits water out of its mouth into a sunken pool (
covered with wire grid and stones). The water is then recirculated via
the pump, up into the base of the gargoyle then back out of its mouth.

We saw the same set up in a local stockist and the gargoyle was sitting
on the ground, throwing water out about 14 inches from its mouth. We
wanted it to sit higher so the stockist ( who casts all their own
products from concrete ) threw together a large upturned planter made
of concrete and sat the gargoyle on it. Turns out he had never done
this before i,e sat it up higher so it was a bit of trial and error for
him

Connected it all up. Put the 12v pump into the plastic pond and turned
on. Water came out about 3 inches then started to drop. It barely
cleared the planter base and just made it into the pool. Given the
plastic bucket is about 14 inches by 30 inches and the gargoyle sits at
the end of it, I was looking for a throw of around 15 to 20 inches to
hit the middle of the pool.

So back to the shop and he gave us a 750 litre and hour pump..We
originally had been given a 650 lph. No difference.

Upto a 1500 lph.. No noticeable difference

Now onto a 2000 lph and it still just about makes the pond but not by
much!! The shop owner is stumped...The plastic pipe going from the
pump to the gargoyle is about 12 mm diameter. The connector coming out
of the pump is about 20 mm diameter so I have used lots of gaffer tape
to make up the difference. No leaks there.

The gargoyle has what looks like thinwall copper pipe inside the cement
casting - placed in there before pouring. It looks like old microbore
copper pipe for central heating.

If I take the pipe directly from the pump and hold it beside the
gargoyles exit hole ( 1.2 metres above the pump ) it lands just about
where I wanted it. Stick it into the gargoyles base and it falls short
by about 10 to 12 inches??

Given this pump is meant to be shifting about 2000 lph then is it to do
with the diameter of the plastic piping and diameter of tube inside the
gargoyle that is creating the restriction?? Any ideas why I have
noticed almost zero difference between a 650 lph pump and a 2000 lph
pump??

I have worked around this temporarily by squeezing the copper tube at
the exit point with pliers and this has the effect of firing a thinner
stream of water into the correct part of the pond but it just isn't
perfect.

Any clues or tips?

Thanks

Ged