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 sys
input = sys.stdin.readline

def solve():
    n=int(input())
    L=list(map(int,input().split()))
    if len(set(L))==1:
        print(-1)
        return
    val = max(L)
    for i in range(n):
        if L[i]==val:
            if i-1>-1 and L[i-1]<L[i]:
                print(i+1)
                break
            if i+1<n and L[i]>L[i+1]:
                print(i+1)
                break
    else:
        print(-1)


if __name__=="__main__":
    for _ in range(int(input())):
        solve()

