It sounds exactly how I described in terms of risk. Effectively you are putting up 15 USDC for maintaining an 85 USDT short. Your money at play is 15 USDC, and you can lose 100% of that amount.
The fact that it sounds like you have to show 100usdc to do the trade is irrelevant as you can do this trade multiple times to build whatever position. In a traditional equities setting they skip the “show 100 USDC then remove 85 usdc” by just saying that margin maintenance for an 85 usdt short is 15 usdc. When people talk about potential losses it is the 15 USDC that matters, not the 100 USDC you need to cycle (because 100 USDC is more of a mechanical inconvenience of not having a real brokerage offered short, not money at play).
The fact that it sounds like you have to show 100usdc to do the trade is irrelevant as you can do this trade multiple times to build whatever position. In a traditional equities setting they skip the “show 100 USDC then remove 85 usdc” by just saying that margin maintenance for an 85 usdt short is 15 usdc. When people talk about potential losses it is the 15 USDC that matters, not the 100 USDC you need to cycle (because 100 USDC is more of a mechanical inconvenience of not having a real brokerage offered short, not money at play).