1. The maximum odds you will accept. If the odds are greater than this then you won't be matched.
2. Your liability. Therefore when matched the stake will be adjusted to equal this liability based on SP. The minimum Betfair will accept is £10.
The basics of what I'm trying to do is this: Assume I have a profit of £20 on a selection. If certain criteria are met, I will fire a LAY bet. If these criteria are not met, I want to take my chances with the SP.
In this case LAYSP is not the trigger you want. If you want your bet to be matched at SP if it is not matched before the off then you should use LAY-SP. In this case the odds and stakes columns simply specify the stake and odds you are placing the lay bet at. If it's not matched before the off then it will be matched at SP providing the liability is at least £10.