Difference in Margin in code VS margin-calculator Page

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Today i see some issue with the Margin Calculator:
For OrientBank Symbol, when i calculate the Margin it came to 6.363. But in Margin Calculator page it is showing as 4.
https://zerodha.com/margin-calculator/BracketCover/

Symbol: OrientBank
Price: 75.75
SL: 0.85 = 74.9
CO LOWER: 4
CO UPPER: 7
Margin in Code: 6.363
Margin in Margin Cal Page: 4
Call: Buy
Type: BO

I didn't observe any difference for other scripts. The same code i'm using it for long time.

    co_lower = co_lower/100
    co_upper = co_upper/100

    trigger = price - (co_upper * price)

    if sl < trigger:
	sl = trigger
    else:
	trigger = sl

    x = 0
    if transaction_type == 'Buy':
	x = (price - trigger) * quantity
    else:
	x = (trigger - price) * quantity

    y = co_lower * price * quantity
    margin = x if x > y else y
    margin = margin + (margin * 0.2)