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=[int(x) for x in input().split()]
    l=[]
    ma=-1
    inx=-1
    for i in range(n):
        if L[i]>=ma:
           ma=L[i]
    for i in range(1,n):
        if(L[i]==ma and L[i-1]<L[i]):
            l.append(i+1)
    for i in range(n-1):
        if(L[i]==ma and L[i]>L[i+1]):
            l.append(i+1)
    if(len(l)!=0):
        print(l[0])
    else:
        print(-1)