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

import math
for _ in range(int(input())):

    n = int(input())
    ar = list(map(int,input().split()))


    p = list(set(ar))
    if len(p) == 1:
        print(-1)

    else:
        
        p = max(ar)

        for i in range(n):
            if ar[i] == p:

                if i == 0 :
                    if ar[i+1] < ar[i]:
                        print(i+1)
                        break
                elif i == n-1:
                    if ar[i-1] < ar[i]:
                        print(i+1)
                        break
                    
                elif ar[i-1]< ar[i] or ar[i+1] < ar[i]:
                    print(i +1)
                    break
