Charting Drawdown

I've attached the essential part of a worksheet which tracks trades. Each trade has a high, and low. (For purposes of my questions I am only discussing the"lows").

Because trades often "overlap" in time it is difficult for me to get the sum of all lows of all open trades at any one time.

I've attempted to do this using this sumifs formula:

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However as you'll see in the attached worksheet, in which I've created an hour-by-hour table, the formula isn't working as I intended.

(To restate my objective: I want to track the actual drawdowns of all open trades on an hourly basis. I don't want the Maximum drawdown using the MIN function.)

Any advice?
Thanks.