oil sight glass almost impossible to gauge

[darrsi]

You don't check the oil until you've run and coated the engine first, which is why your egg cup theory is really not a theory at all, 'cos if you were to wait another 20 minutes the oil will rise and rise 'til you can't see a level.
If you are not starting the engine, which is sounding increasingly likely by the sounds of it, then you do not have enough oil in your engine.
Hence the reason your oil light comes on!

My oil light only came on for an instance on hard accelerating and after a year and 1000 miles.
I see what you are saying about starting the engine to splash your bits with oil and then let it settle, but once you have chucked in 2.5 ltrs - you know that is in there, and then you pour in a bit at a time to get your level -- how much (i wonder) is there going to be used up coating your coggs.
Anyway I spose I do actually start the engine cos when I have filled I go for a quick spin -wait to cool down and then check and top up if needed.

Waiting for it to cool down just throws everything i said out of the window.
Wait for the level to settle, we're talking seconds, not minutes.