Just remember that the electronic dip stick will not recognise any top up less than 0.5L. At least this is true for my M6, it actually says this in the handbook too.
However I have noticed with my 630i that it reacts much better to lower top up amounts.

I don't know why there is different behaviour between the two as the oil level sensor is common across a lot of models (1, 3, 5, 7, all engine sizes):

http://bmwfans.info/parts-catalog/12617607910/

Both the N52 in the 630i & the S85 in the M6 use oil between services. I think that is true with most BMW engines.

BMW quote 600 miles/litre for the N52 as an acceptable threshold. But I think the reality should be much less usage in most cases.