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())
    l = list(map(int,input().split()))
    m = max(l)
    ans = 0
    flag = 0
    if l[0]==m and l[0] > l[1]:
        ans = 0
        flag = 1
    if l[n-1]==m and l[n-1]>l[n-2]:
        ans = n-1
        flag = 1
        
    if flag==0:
        
        for i in range(1,n-1):
            if l[i]==m:
                if l[i]>l[i-1] or l[i]>l[i+1]:
                    ans = i
                    break
    if flag ==0 and ans==0:
        ans = -2
    print(ans+1)
    