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 _ in range(t):
    n = int(input())
    l = list(map(int,input().split()))
    maxp = l[0]
    minp = l[0]
    minpi=0
    maxpi=0
    for i in range(1,n):
        if l[i]>=maxp and (l[i-1]<l[i] or  (i!=n-1 and l[i+1]<l[i])):
            maxpi=i
            maxp = l[i]
        if l[i]<minp:
            minpi=i
            minp = l[i]
    if maxp==minp:
        print(-1)
    else:
        print(maxpi+1)
        
        
        
        
        
             
