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

t=int(input())
for i in range(t):
    n=int(input())
    arr=[int(x) for x in input().split()]
    
    if len(set(arr))==1:
        print(-1)
        continue
    
    m=max(arr)
    
    for i in range(n):
        if i==0:
            if arr[i]==m and arr[i+1]<m:
                print(i+1)
                break
        elif i==n-1:
            if arr[i]==m and arr[i-1]<m:
                print(i+1)
                break
        else:
            if arr[i]==m and (arr[i+1]<m or arr[i-1]<m):
                print(i+1)
                break
    