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())
    
    fishlist = list(map(int, input().split()))
    
    check = list(set(fishlist))
    
    if len(check) == 1 :
        print(-1)
    else :
        bigfish = max(fishlist)
        domi = -1
        
        for i in range(n) :
            if i == 0 and fishlist[i] == bigfish :
                if fishlist[i] > fishlist[i+1] :
                    domi = i+1
                    break
            elif i == n-1 and fishlist[i] == bigfish :
                if fishlist[i] > fishlist[i-1] :
                    domi = i+1
                    break
            else :
                if fishlist[i] == bigfish :
                    if fishlist[i] > fishlist[i-1] or fishlist[i] > fishlist[i+1] :
                        domi = i+1
                        break
        print(domi)