Once listed, de-listing occurs when share price falls below $1. There are multiple buffers in the process to ensure a short-term dip below $1 doesn't result in the stock being de-listed.

At a target price of $4, you're talking about a 75% drop in share price before de-listing becomes a concern. I see that as excessive and unnecessary. And I don't care about anyone wanting to buy on margin. That's another risk in itself, and certainly not one to take if one needs extra price buffer to ensure a de-listing doesn't occur. Buying on margin is a good way to lose all your shares and more money than you have invested in cases where the price drops substantially... as in excessive shorting of a stock right after they up-list to Nasdaq.