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())
    p = tuple(map(int, input().rstrip().split()))
 
    flag=0
    if n==1:
        print(-1)
    else:
        m = max(p)
        for i in range(n):
            if p[i]==m:
                if i==0:
                    if p[1]<m:
                        print(1)
                        flag=1
                        break
                elif i==n-1:
                    if p[n-2]<m:
                        print(n)
                        flag=1
                        break
                else:
                    if p[i-1]<m or p[i+1]<m:
                        print(i+1)
                        flag=1
                        break
    if flag==0: print(-1)
    
    