rear hatch strut question

Not haven had a tinroof (4 door) before, only a caddy, I am wondering if the strut I bought, new, is working properly.
It's strong enough to hold the hatch open but not to lift it on its own!
Is this normal? Or do I have a bad strut (got it from veedubmachine)

Should lift it ok. Having just one strut is a design flaw, MK2s have 2 and so do most other cars.

It will not lift or do it slowly if;
strut is old
hatch has spoiler fitted (esp to lower part of tail gate)
weather is cold (gas in struct contracts)
hatch hinges are stiff
any combo of the above