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())
    a = [int(i) for i in input().split()]
    if len(set(a)) == 1:
        print(-1)
    else:
        maxi = 0
        maxel = a[0]
        colmax = 1
        for i in range(1, n):
            if maxel < a[i]:
                maxel = a[i]
                maxi = i
                colmax = 1
            elif maxel == a[i]:
                colmax += 1
        if colmax > 1:
            maxi = -2
            for i1 in range(1, n):
                if a[i1] == maxel and a[i1-1] < maxel:
                    maxi = i1
                    break
            for i1 in range(n-1):
                if a[i1] == maxel and a[i1+1] < maxel:
                    maxi = i1
                    break
        print(maxi+1)
