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())
    arr=list(map(int,input().split()))
    count=0
    c=0
    for i in arr:
        if i==arr[0]:
            count+=1
    d=max(arr)
    flag= False
    for i in range(n):
        if arr[i]==d and not flag:
            if i==0 and (arr[i]>arr[i+1]):
                c=i
                flag=True
            elif i==n-1 and (arr[i]>arr[i-1]):
                c=i
                flag=True
            elif i>0 and i<n-1:
                if (arr[i]>arr[i-1]) or (arr[i]>arr[i+1]):
                    c=i
                    flag=True
            


    if count==n:
        print(-1)
    else:
        print(c+1)