Intraday margin rates from futures brokers

I think I have a decent grasp on how initial margin, margin calls and maintenance margin work, but FCMs/brokers add their own intraday margin rate, and I need to clarify exactly how to calculate the number of ticks or percent moving against me to activate margin call.

Why do some brokers only have a $40 intraday margin for MES? Doesn’t this increase the leverage to about x500, meaning just one tick moving against you will margin call? Furthermore some brokers like amp don’t state the corresponding maintenance margin. Here’s my current understanding with a solid example.

No intraday margin rate:
-Bob buys long 1 MES contract at initial margin of $1000. MES quote is at 4000points. So it’s worth $5×4000=$20,000

-This means his leverage is 20x

-Let’s say there is a 10% difference between initial and maintenance margins

10% /20 = 0.5%

Therefore if MES quote drops by 0.5%, i.e. it reaches 3980, margin call will be activated.

Now how does the addition of an intraday margin rate change this calculation?