the logic of the FixedSlippage eludes me.

The transaction price is calculated once we've added up all of the open orders.

what if we have a long trade and a short trade for the same number of shares
I think I am confused about direction and pricing on individual orders
vs
the direction and pricing on multiple orders (outside of the for order in orders)

should fixed slippage do partial fills like volume share slippage?
or are we assuming unlimited number of shares?
(would it be better to limit it to the volume of that bar?)