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())):
    aq = int(input())
    arr = list(map(int, input().split()))
    s = set(arr)
    if (len(s) == 1):
        print(-1)
    else:
        mx = max(arr)
        for i in range(len(arr)):
            if arr[i] != mx:
                continue
            if arr[i] == mx and i == 0:
                if arr[i+1]<mx:
                    print(i+1)
                    break
            elif arr[i] == mx and i == aq-1:
                if arr[i-1]<mx:
                    print(i+1)
                    break
            elif arr[i] == mx:
                if arr[i-1]<mx or arr[i+1]<mx:
                    print(i+1)
                    break