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(int(input())):
    x = int(input())
    r = [int(x) for x in input().split()]

    if len(set(r))==1:
        print(-1)
    else:
        max_t = max(r)
        for i in range(0, x):
            if r[i]!=max_t:
                continue
            if(i>0):
                if r[i]>r[i-1]:
                    print(i+1)
                    break
            if(i < x-1):
                if r[i]>r[i+1]:
                    print(i+1)
                    break