Miners are economically incentivized to sort the transactions by gas price descending, because it can increase their income. But they can sort and prioritize the transactions in whatever way they want, and use whatever algorithm they want. For this reason, I don't think you can make 100% foolproof predictions about this situation.
Statistically, I would imagine that the smaller the transaction, the more likely it is to be included sooner, because it leaves some room in the block for transactions with a higher gas price.
Depending on the exact sorting algorithm that miners use, if you are transmitting full-block-transactions, it may be necessary to use a high gas price to out-compete all the other transactions in the mempool.
I hope this helps.