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())):
    n=int(input())
    a=list(map(int,input().split()))
    maxx=max(a)
    minn=min(a)
    if maxx==minn:
        print(-1)
    else:
        for i in range(n):
            if a[i]==maxx and i==0:
                if a[i+1]<a[i]:
                    print(i+1)
                    break
                else:
                    continue
            if a[i]==maxx and i==n-1:
                if a[i-1]!=a[i]:
                    print(i+1)
                    break
                else:
                    continue
            if a[i]==maxx and (a[i-1]<maxx or a[i+1]<maxx):
                print(i+1)
                break