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 mi():return (map(int,input().split()))
for _ in range(int(input())):
    n=int(input())
    arr=list(map(int,input().split()))
    m=max(arr)
    if arr.count(m)==n:
        print(-1)
    else:
        i=0
        while i<n:
            if arr[i]==m:
                if i==0:
                    if arr[i+1]!=m:
                        print(i+1)
                        break
                elif i==n-1:
                    if arr[i-1]!=m:
                        print(i+1)
                        break
                else:
                    if arr[i-1]!=m or arr[i+1]!=m:
                        print(i+1)
                        break
            i+=1