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())
    prn = list(map(int, input().split()))

    if len(set(prn)) == 1:
        print(-1)
        continue
    idx, maixmum = 0, max(prn)
    for i in range(1, n):
        if prn[i] == prn[i - 1]:
            continue
        elif prn[i] > prn[i - 1]:
            idx = i + 1
        else:
            idx = i
        if prn[idx - 1] == maixmum:
            print(idx)
            break