Hi Night Guy, i sent you a message about this roughly 2 years ago but you never got back to me, whether you missed it don’t know. I know you do get a lot of questions off other players so you probably don’t get the time to reply to every message or you might have thought what the heck is this mad old woman going on about lol !!!
I have been doing this for about 3 years now and get lots of stacked prizes out of the green boxes, i clear them every 7 days on a Sunday. I have only got 30 L4 monuments at the moment so not getting as much as you regarding PP’s and Gems.
I have noticed though, to get more green prize boxes you do have to empty your city coins every 6 hours if you can i empty my city coins 3 times per day.
I have been doing lots of observations over the last few years.
Thank you for all the useful information you post on the forum, it is appreciated by lots of players on CW.
Keep up the good work 
I