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

import collections
t=int(input())
for q in range(0,t):
    n=int(input())
    a=[int(i) for i in input().split()]
    d=collections.Counter(a)
    if len(d)==1:
        print(-1)
    else:
        index=-1
        m=max(a)
        for i in range(0,n-1):
            if a[i+1]<a[i] and m==a[i]:
                index=i+1
                break
        if index==-1:
            for i in range(1, n):
                if a[i -1] < a[i] and m == a[i]:
                    index = i + 1
                    break
        print(index)