What should Oil Pressure be at Idle when Hot for a 1.8 L-Jet?

Mine idles at about 0.75 Bar ( 10.8 PSI) after driving in traffic.
Which I assume is too low , as the Green light comes on.
At cold start I see 1.5 Bar (21 PSI).

I am using a VDO 5 Bar gauge ( from late 80's VW Golf Cabrio) and matching sender. Sender is fitted to stock Oil Press Light switch location, via a braided SS hose.

I have a recent oil change ( 40W ) and idle is about 1000 rpm.

I am contemplating fitting the Weltmeister Oil Pressure Boost Piston kit.
Anybody have experience with this product?

Thanks

Cold Start ............. 20 PSI ?
What is the ambient temperature ?

Another alternative.
http://www.tangerineracing.com/oilpressurerelief.htm
Either way I'd talk to Chris. My .02c.

Thanks for the info.
I used "cold start" incorrectly. I meant once the engine had cooled down. Ambient temp about 34 C ( approx 93 F )

The stock pressure switch opens between 2-6psi. The aftermarket ones open at 12psi. So technically, you're above the stock recommendation. The factory manual recommends a 'wear limit' of 28psi @ 2500 rpm with the oil at operating temp.

The oil you use (not just weight, but brand as well) can have a significant effect on the pressure reading.

All that being said, I think Chris' upgrade piston is a great investment.