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