Storage Pool cannot allocate free space to a virtual disk

i have storage pool in windows server 2012 made of 3 x 3tb disks. total capacity 8.18tb. there thin provisioned virtual parity disk of 7tb 4.87tb allocated.

server manager shows 900gb of free space available in pool.  each of 3 physical disks shows 2.44tb used , 300gb free.

i trying create new fixed simple disk of remaining space. should able create virtual disk of 900gb.

the maximum size of fixed simple disk can create 288gb (i tried server manager , powershell this). disk properties show equally divided across 3 physical disks (96gb x 3). after creating vhd,  free space each physical disk shows 204gb. free space pool shows 612gb.

any assistance in understanding these numbers, , makng use of full space available, appreciated.

sorry,

i misunderstood original question. if have equal free space on (3) drives, should able create simple space 3 column , size equal sum of available free space in pool. can share output of following powershell commands?

get-storagepool | ? isprimordial -eq $false | ft friendlyname,size,allocatedsize -autosize
get-storagepool | ? isprimordial -eq $false | get-physicaldisk | ft friendlyname,size,allocatedsize,manufacturer,usage  -autosize
get-virtualdisk | ft friendlyname,resiliencysettingname,numberofcolumns,numberofdatacopies,size,allocatedsize,footprintonpool -autosize

Windows Server  >  Windows Server 2012 General