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 _ in range(t):
    n = int(input())
    a = list(map(int,input().split()))
    if len(set(a)) == 1:
        print(-1)
        continue
    mx = max(a)
    flag = True
    for i in range(n):
        if a[i] == mx:
            if i == 0:
                if  i+1 < n and a[i+1] < a[i]:
                    flag = False
                    print(i+1)
                    break
            elif(i == n-1):
                if i-1 >=0 and a[i-1] < a[i]:
                    print(i+1)
                    flag = False
                    break
            else:
                if a[i-1] < a[i] or a[i+1]  < a[i]:
                    print(i+1)
                    flag = False
                    break
    if flag:
        print(-1)