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 = [int(x) for x in input().split()]
    if len(set(l))==1:
        print(-1)
        continue
    m = max(l)
    ind = 0
    for i in range(n):
        if l[i]==m:
            if i>0 and l[i-1]!=m:
                ind = i
                break
            elif i<n-1 and l[i+1]!=m:
                ind = i
                break
    print(ind+1)