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