Locational Marginal Pricing when different prices and when the same?
okay meanwhile I got the answer to this:

the main idea behind LMP is to reduce the marginal cost of the WHOLE system.... therefore it is cheapier if you select those offers that way....

calculations:

38 * 600 + 48 * 600 = 51600

if we would do it as I thought makes more sense:

36 * 400 + 48 * 800 = 52800

as you can see even though the price seems to be more fair for node 1 now in total the costs increased from 51600 dollars to 52800 dollars