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

cases = int(input())
for t in range(cases):
    n = int(input())
    a = list(map(int,input().split()))
    a1 = list(set(a))
    if len(a1)==1:
        print(-1)
    else:
        m = max(a)
        mis = [i for i in range(n) if a[i]==m]
        for i in mis:
            if (i>0 and a[i-1]!=m) or (i<n and a[i+1]!=m):
                print(i+1)
                break