How to divide bandwith equally

Hi to all,

I would to allow the same bandwith  to each user. Consider I have a Fortigate with 2 interfaces, wan1 and ether1. All user are connected in a private network under ether1 and go to internet using wan1 interface at 100 Mbps (in up and down). I have a policy that allow this traffic that have input interface ether1 and output interface wan1. In the same policy I tried to apply traffic shaping with these problems:

1) I create a shared traffic shaping (also reverse shaping) with maximum bandwith of 50 Mbps ( I would to preserve the remaining bandwith for other use) and in this way the total traffic from lan to internet is 50 Mbps. If in the lan there is only one user it use all 50 Mbps. But if an user are downloading for example at 50 Mbps and a second user try to access to internet (for a download) I would both users have 25 Mbps available. In real case, instead, the first user continue to go at 90% of 50 Mbps and the second user use only 10% of remaining bandwith. Why ?  

2) I tried to create a per ip shaping with maximum bandwith of 50 Mbps. In this case each user can use 50 Mbps. Then if I have 2 users they can use 100 Mbps (the totatl bandwith available)

In which way can I have an equal bandwith for each user ?

Thanks in advance.