Hi @robhaisfield.
First a remark, when having as collateral both ETH and USDC, your LTV and liquidation thresholds are actually a combination of the ones of ETH, USDC, weighted depending on the proportion of amounts of each forming your collateral. ETH and USDC happen to have the same parameters, but for the sake of understanding.
Concerning your question about liquidation, the rule is that up to 50% of the total value of your collateral gets liquidated, and it is the liquidator who chooses which asset to receive. So if you enter in liquidation (health factor below 1), taking into account your example, the liquidator could choose to take part of your ETH (as it is more than 50% of your collateral), or just the whole USDC. In this case it is probably smarter to choose the first, to liquidate and take bonus in as bigger amount as possible.