Requiring the initial position to be below the safety LTV threshold is to protect users from immediate liquidations. The Debt Share Value, represents the amount of outstanding tokens the borrower owes, and is the principal borrowed plus accrued interest to be paid. The Collateral Size is the amount of collateral that is posted for the position. For example, say you used 1000 $USDC (assuming 1 USD) to initiate a borrow position for an A tier asset. Given the current configuration, you would be able to borrow 0.9 * 0.65 * 1000 = 585 USD worth of that asset at most upon initiating a position.