In my IBKR account if I currently have a position of short 5 Nasdaq Micro contracts and then I bought an EMini Nasdaq would I automatically end up with a position of Long 5 Micros? I suppose I could try it but thought I'd ask initially.
Yes. You can trade into a position with micros, and then trade a mini against the position or hedge a mini with micros. For example, say you want to daytrade a position of half a mini. You can trade into a 5 lot on micros, and then trade the mini against the position during the day. The fewer micros you end up doing, the lower your commisions will be due to the mini being relatively cheaper to trade (per dollar of notional exposure). There will still be a small margin even if the contracts are perfectly hedged. With IBKR, you can do the same thing with Nikkei futures on the Japanese market. https://www.jpx.co.jp/english/derivatives/products/domestic/225mini/01.html
FALSE! TRUE Fungibility is usually connected to contract expiration/contract settlement. At other times, the 2 instruments (mini and micro) remain as open positions, unless further instruction and approval is given. If applicable, by necessity, liquidation would also invoke the fungible feature.
I was hoping they would automatically 'collapse' offsetting positions into a net +5 micro position. From the comments here it appears that's not the case.
It is not an offsetting position. It is, basically, 15 micro contracts open, with margin requirement on all sides. The only offset you get is the fact that they move in tandem.
No, IBKR does not offset positions. To them those mini's and micro's are two different financial instruments which are handled independently of each other.