Yes, it does, Steel Penny. My Margin use is limited but I'd like to have it available when needed. I maintain and trade also stocks above $5 in my Margin Account. As far as I know, it seems it applies to all three exchanges for it's based on price value of the stocks. The percentages of course are subject to change.
From a check I see Non-Margin Buying Power shows only 30% of what is available to me in the Margin Buying Power.
The overall state of one's positions and values of the stocks and their relative balance & proportions obviously impact what's available or due to them as by a Margin Call.
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