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

def ans(a, n):
    if max(a)==min(a):
        return(-1)
    
    t = [a[i] for i in range(n)]

    for i in range(n-1):
        if t[i]>t[i+1]:
            t[i]+=1

    for i in range(n-1,0,-1):
        if t[i]>t[i-1]:
            t[i]+=1

    ind = -1
    maxm = -1

    for i in range(len(t)):
        if t[i]>maxm:
            maxm=t[i]
            ind = i+1

    return(ind)

m = int(input())

for j in range(m):
    n = int(input())
    arr = input().split()

    a = []

    for i in arr:
        a.append(int(i))

    print(ans(a, n))
