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 cnt in range(int(input())):
    n = int(input())
    b = list(map(int, input().split()))
    m = max(b)
    if min(b) == max(b):
        print(-1)
    
    else:
        for i in range(n):
            if b[i] == m:
                if i == 0:
                    if b[i] > b[i+1]:
                        print(i+1)
                        break
                elif i == n-1:
                    if b[i] > b[i-1]:
                        print(i+1)
                        break
                else:
                    if b[i] > b[i-1] or b[i] > b[i+1]:
                        print(i+1)
                        break
