For auto-lend, I actually just read there "how it works"
http://www.geekzone.co.nz/forums.asp?forumid=48&topicid=196490&page_no=5
"""
The Auto-lend engine prioritises which Lender it orders notes for first using a prioritisation ratio of 'Funds available' to 'principal outstanding +1'. The Lenders with the highest ratio will get the first orders of notes. For example:
- Lender A has $50 Funds available and $1,000 Principal Outstanding, so a ratio of 5% (50 / 1001)
- Lender B had $300 Funds available and $8,000 Principal Outstanding, so a ratio of 3.75% (300 / 8001)
- Lender C has $8,300 Funds available and $187,800 Principal Outstanding, so a ratio of 4.41% (8,300 / 187,801)
"""
So, more principal outstanding (more invested) - the less priority you get.
eg. Say I have 15,000 outstanding, and I have $25 available = ratio of 0.166% - not very likely going to get auto-lended.
Not sure when I will stop auto-lending.
My eventual plan would be to just change my program to withdraw interest earned only (keep outstanding principal constant).
That way the investment remains constant and so should the interest return.