One thing you need to watch with the PFG Best simulator is that it is very good at giving you good fills. This is specially important if you are scalping for just a few ticks. In fact, it makes the difference between profitable and unprofitable trades.
Here is what I mean. If the NQ is Bid 1380.00 / Ask 1380.50, and in the real world you put a market order in to Buy, you will be filled at 1380.50. You immediately sell at market, you will get 1380.00, and you have lost .50.
The PFG Simulator does not discriminate between bid and ask and fills you at the last price whether you are buying or selling. This does not make much of a difference if you are trading for several points per trade, but as you indicated, you are scalping for a few ticks. Then the it makes a huge difference.
I could make millions on the PFG simulator by simply trading in a slow, choppy market. All I have to do is wait for someone to buy (Last price goes up to 1380.50) and hit the sell button. I get filled on that price, then wait for someone to buy (Last price goes down to 1380.00) and hit the sell button. It's like free money. But the real world doesn't work that way!
The only you can sell at the ask price and buy the bid is to have a limit order already in the system. If the market is currently at this price (1380.00 / 1380.50) you will notice in the depth of market are listed the number of contracts available at this price. These are limit orders already submitted. If you put a limit order in to sell at 1380.50 you go to the back of the line, and only after all the other limit orders are filled at that price are you filled. It may happen, but likely the market will move on before you get filled. For scalping purposes, you must plan to always sell at the bid an buy at the ask. If you do better than that, you're lucky, but don't count on it.
I think this is the answer to your "what am I missing" question.
Cheer,
kp