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 i in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    if len(set(l))==1:
        print(-1)
    else:
        k=max(l)
        for i in range(n):
            if l[i]==k:
                if (i-1)>=0 and l[i-1]<k:
                    print(i+1)
                    break
                elif i+1<n and l[i+1]<k:
                    print(i+1)
                    break
