OOP: Invisibility Cloak/Sirius

[dreambeliever001]

No: HPFGUIDX 69727

I'm in the middle of reading OOP for my third time when something 
struck me as kind of strange. I don't understand why Sirius could not 
help the order.  When Mundungus and all the other members of the 
Order were keeping an eye on Harry they used an Invisibility Cloak. 
Why couldn't have Sirius also used the cloak not only to help the 
order but to keep an eye on Harry?  He wouldn't have been seen by 
anyone and yet he would of felt as if he was doing something 
important for the Order.  I don't know, just a thought.   Diana