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

if __name__ == "__main__":
    t = int(input())
    while t>0:
        t-=1
        n=int(input())
        arr = list(map(int, input().split(' ')))
        max_ele = max(arr)
        if arr.count(max_ele) == len(arr):
            print("-1")
        else:
            for i in range(len(arr)):
                if arr[i] == max_ele:
                    if i == 0 and arr[i+1]<arr[i]:
                        # print("A")
                        print(i+1)
                        break
                    elif i == (len(arr)-1) and arr[i-1]<arr[i]:
                        # print("B")
                        print(i+1)
                        break
                    elif i!=0 and i!=len(arr)-1 and (arr[i]>arr[i-1] or arr[i]> arr[i+1]):
                        # print("C")
                        print(i+1)
                        break