bpdulog

say you are a large cap manager ... so you can select a benchmark with a large cap focus and have 3 index options to consider of which:
- LC index 1 has 1000 stocks
- LC index 2 has 100 stocks
- LC index 3 has 20 stocks
I say the manager would be better off selecting the 1000 stock index as his benchmark as it is more likely to cover a wider range of stocks in Large CAp domain from which you can be expected to select your stocks for your portfolio.

as regards +ve active positions, if your benchmark is appropriate, normally you are not expected to hold all index stocks but a sample that represents best of opportunity in large cap space. say out of 1000 stocks you hold a sample of 150 stocks (that according to you will outperform the market in near future) ... so ideally if you are holding just 150 stocks instead of all 1000, you can expect to hold then in greater weights than they are in the index or a +ve active weight.

hope its clear somewhat.