1. I have proportional mining and have 1380Mhash according Guiminer, according http://www.alloscomp.com/bitcoin/calculator.php I should be getting 28bitcoins/month.
But I have now mined 24/7 for a couple of days and according my own calculations I'm about 20bitcoins/month this calculation is confirmed by the deepbit site which says I have 0.65bitcoins last 24h.
What could cause me mining 20bitcoins instead of 28bitcoins with 1380mhash?
2. My understanding is that the proportional mining takes 3% fee, considering deepbit has wery high pool rate my understanding is usually the variance should be low on mined bitcoinst in relation to my mhash, so it should be around 28bitcoins?
3. Besides the 3% fee are there other fee's aswell?
For example, during the last 2 weeks our average luck was somewhere about 4% better than expected.
You aren't "mining 20 bitcoins" unless you tried to mine all the month.
2. No, there are no other fees.