Hi,
There is no such thing as a magnetic monopole. Every magnet made or found in nature to date has two poles, one usually called "north" and one usually called "south".
For an electromagnet, an increase in the distance between faces increases the reluctance which means less strength. So if the core as is has faces 2 inches apart and after cutting one leg off the two faces are 3 inches apart, the one with the 2 inches apart should be stronger.
If could somehow get the two faces to be closer together than you would have a better electromagnet. Say 1 inch apart. That should pick up smaller pieces better. If you cant do that, try extending one face outward toward the other somehow.
An idea would be to make a straight piece like the "I' of the original core that is only 1/2 as long as it would take to go across all three faces. Then it would go across only two faces, and if you make a gap of say 1/2 inch at one face then it should pick up smaller pieces better.
something like this:
Code:
|-----------------
| ----------- |
| | | |
| | | |
| | | |
| --------- | |
|------------ | |
gap
(i might have to come back and draw this out better)