Market on Close orders and fills

My trading system trades US equities during regular trading hours.
In real life I trade the system with market on close orders. They are on TD Ameritrade and interactive brokers - which is what I use.
On C2 the best I can do is submit a market order for 15.59 - which often is off quite a bit on fills. (it can be off 1% - as in on a 3000$ position size the difference between my entry/exit and resulting profit versus the C2 entry/exit and profit is often over 30$.)
Is there a better way to issue Market on Close orders?
Alternatively - if I do Market on Open - is that supported better? (as in will it take the official open price?)

As far as I know there is no market on open feature at C2. Your market order fill will be close but not the same as a market on open order in my experience.