Margin Requirements TSX listed equities require 30% margin posted if trading at $5.00+
The margin requirement jumps to 50% if share price drops below $5.00 (unmarginable if below $3.00)
I am not sure how quickly the incremental margin is requested by any given brokerage firm. This margin requirement seems standard across various brokerage firms and would be common knowledge. The shorts may force the price to this point to trigger additional selling.
Just a thought.