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 t in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    if len(set(a)) == 1:
        print(-1)
        continue
    mx=max(a)
    for i in range(n):
        if 0 < i < n-1:
            if a[i]==mx and(a[i-1]<mx or a[i+1]<mx):
                print(i+1)
                break
        elif i > 0:
            if a[i]==mx and a[i-1]<mx:
                print(i+1)
                break
        else:
            if a[i]==mx and a[i+1]<mx:
                print(i+1)
                break