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 i in range(int(input())):
    n = int(input())
    lis= [int(x) for x in input().split()]
    if(lis.count(lis[0])==len(lis)):
        print(-1)
        continue
    m = max(lis)
    x=0
    for i in range(n):
        if(lis[i]==m):
            if(i>0):
                if(lis[i-1]<m):
                    x=i+1
            if(i<n-1):
                if(lis[i+1]<m):
                    x=i+1
            
    print(x)