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):
    ans=0
    n = int(input())
    a = list(map(int, input().split()))
    res = True
    res = all(ele == a[0] for ele in a) 
      
    if(res): 
        print("-1") 
    else: 
        x = max(a)
        for j in range(len(a)):
            if a[j]==x:
                if(j-1>=0 and a[j-1]<a[j]):
                    ans = j+1
                if(j+1<n and a[j+1]<a[j]):
                    ans = j+1
        print(ans)