amount of line to have on a spinning reel

Question
I am using a Mitchell 300 and a Diawa 7300 spinning reels.  For optimun performance, especially in casting, how full should the spool be.  My intuition says there will be less resistance to the line coming off of the spool if it has less of an angle to go from the level of the coiled line to that of the eyelets on the pole.  Thank you for your time sir

Answer
This question is kind of out side of my expertise but I will give you my opinion.

In spinning reels, the reason you don't want to spool up all the way to the edge is to prevent line from peeling off the spool when you don't want it to. At least that is what I have heard.

In reality, the brand and type of line has more to do with this than any thing else. I use Cabelas "Pro line" mono (recently I have switched to Cabelas "Pro line" co-polymer) almost exclusively on spinning reels as it does not try to come off the spool when you don't want it to.

So in my opinion, fill it up to the rim and try it for one trip, if it is still coming off the spool when you don't want it to, try another brand/type of line.