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

test = int(input())
for _ in range(test):
    n = int(input())
    arr = list(map(int, input().split()))
    arrv = []
    for i in range(n):
        arrv.append((arr[i], i))
    
    arrv.sort(reverse = True)

    if arrv[0][0]==arrv[-1][0]:
        print(-1)
    else:
        v = arrv[0][0]
        for i in range(n):
            if arr[i]==v:
                if i==0 and arr[i+1]<v:
                    print(i+1)
                    break
                elif i==n-1 and arr[i-1]<v:
                    print(i+1)
                    break
                elif 0<i<n-1:
                    if arr[i-1]<v or arr[i+1]<v:
                        print(i+1)
                        break