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 = list(map(int, input().split()))
    b = max(a)
    i = 0
    while i<len(a):
        if a[i] == b:
            if i-1>=0:
                if a[i-1]<a[i]:
                    print(i+1)
                    break
            if i+1<len(a):
                if a[i+1]<a[i]:
                    print(i+1)
                    break
        i+=1
    else:
        print(-1)