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())
    lene = list(map(int, input().split()))
    if len(set(lene)) == 1:
        print(-1)
        
        
    else:
        lene.append(-1)
        j = n
        
        
        if lene[0] > lene[1]:
            j = 0
            
        if lene[n - 1] > lene[n - 2] and lene[n - 1] > lene[j]:
            j = n - 1
            
        for i in range(1, n - 1):
            if lene[i] > lene[j]:
                if lene[i] > lene[i + 1] or lene[i] > lene[i - 1]:
                    j = i
                    
                    
                    
        print(j + 1)
