Cannot use margin to short many stocks - why?

Recently I opened a paper trading account with alpaca. Theoretically I should have 4x buying power due to day trading status. This is true when opening long positions, however when making short positions, trading power often decrease by ~4x implying I cannot use margin to short. The only limit I see to short trading on margin is on stocks less than 5$, but this is not the case for my trades.

Any guidance on why this is happening and if it’s possible to get around this restriction would be much appreciated, or a way to tell when a security cannot be shorted with margin would be helpful. Thanks.