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 i in range(t):
    n = int(input())
    l = list(map(int,input().split()))
    m = max(l)
    if min(l)==m:
        print(-1)
        continue
    for j in range(n):
        if(l[j]==m):
            if(j!=(n-1)):
                if(l[j+1]<l[j]):
                    print(j+1)
                    break
            if(j!=0):
                if (l[j - 1] < l[j]):
                    print(j+1)
                    break