1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t=int(input())
for i in range(t):
     n=int(input())
     a=[int(i) for i in input().split()]
     x=max(a)
     i=0
     b=0
     while i<n:
          if(a[i]==x):
               if(i==0):
                    if(a[i]>a[i+1]):
                         b=1
                         print(i+1)
                         break
               elif(i==n-1):
                    if(a[i]>a[i-1]):
                         b=1
                         print(i+1)
                         break
               elif(a[i]>a[i+1] or a[i]>a[i-1]):
                    b=1
                    print(i+1)
                    break
          i+=1
     if(b==0):
          print(-1)
               
          
               
     
                    
               
          
          

     
          
