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())):
    a=int(input())
    b=[int(i) for i in input().split()]
    f=max(b)
    if min(b)==f:
        print(-1)
    else:
        for i in range(a):
            if b[i]==f:
                if i==0:
                    if b[i]>b[i+1]:
                        print(i+1)
                        break
                if i!=0 and i!=a-1:
                    if b[i]>b[i+1] or b[i]>b[i-1]:
                        print(i+1)
                        break
                if i==a-1:
                    if b[i]>b[i-1]:
                        print(i+1)
                        break