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

for _ in range(input()):
    n=input()
    a=[int(i) for i in raw_input().split()]
    if(max(a)==min(a)):
        print -1
        continue
    maxx=max(a)
    for i in range(n):
        if(a[i]!=maxx):
            continue
        if i==0 and a[i+1]!=maxx:
            print i+1
            break
        elif i==0:
            continue
        elif i==n-1:
            print i+1
        elif a[i]>a[i-1] or a[i]>a[i+1]:
            print i+1
            break
    
