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()]
    
    if a.count(max(a))==n:
        print(-1)
        continue
    
    z=max(a)
    
    if a[0]==z and a[1]<z:
        print(1)
        continue
    
    if a[n-1]==z and a[n-2]<z:
        print(n)
        continue
    
    for i in range(1,n-1):
        if a[i]==z and (a[i]>a[i-1] or a[i]>a[i+1]):
            print(i+1)
            break