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 = input()
    a = list(map(int, input().split()))

    if a.count(max(a)) == len(a):
        print(-1)
        continue

    mx = max(a)
    flag = False

    for i in range(len(a)):
        if i == 0:
            if a[i] == mx and a[i+1] < mx:
                print(i+1)
                flag = True
                break
        elif i == len(a)-1:
            if a[i] == mx and a[i-1] < mx:
                print(i+1)
                flag = True
                break
        else:
            if a[i] == mx and (a[i-1] < mx and a[i+1] <= mx) or (a[i-1] <= mx and a[i+1] < mx) :
                print(i+1)
                flag = True
                break

    if not flag:
        print(-1)
        
