I can’t remember where it was posted but I remember the current spread, at least for NBT/USD, is intentionally set to be the exchange fee.
I think spread, slippage, wall collision cost, loss due to market downtrend etc are all folded into custodian fee currently, however. So they shouldn’t count.
edit: the above is not correct for LPC grant generated by vote, but correct for LPCs who bring their own fund.